Download Biol 212 Zoology Lab 06: Phylum Annelida (10

Biol 212 Zoology
Lab 06: Phylum Annelida (10 points)
Introduction
The phylum Annelida includes the segmented worms, such as earthworms, with
representatives in the marine, freshwater and damp terrestrial environments. The word “annelid”
means “little rings,” and refers to the ring-like segmentation of the body.
There are over 22,000 described species of annelids. Annelids are trochozoans, molecular
studies suggesting the closest living major group being the molluscs; both exhibit trochozoan
larvae. Until recently (2011), the annelids were divided into the class Polychaeta, which included
the marine clamworms, and the class Clitellata, with two subclasses: the subclass Oligochaeta,
which included the earthworms, and the subclass Hirudinea, which included the leeches. Based
on molecular phylogenetics, the annelids are now divided into two clades: clade Errantia and
clade Sedentaria. The Errantians include most of the class Polychaeta, with a few transferred
over to the clade Sedentaria. The clade Sedentaria also includes the Clitellata and its two
subclasses. The former phyla Pogonophora, Echiura and Sipuncula have also been reclassified
under the phylum Annelida.
Annelids are bilateral, protostome worms with a circular cross section. The body cavity
of annelids is a true coelom, but is a schizocoel, formed from a split in the mesoderm. Most
annelids are characterized by metamerism, or the serial repetition of body segments, although
some groups now classified with the annelids do not exhibit this. Each body segment hosts a pair
of excretory organs called nephridia that drain the preceding body segment. The body segments
are fluid-filled, forming a turgid hydrostatic skeleton; by contracting and relaxing longitudinal
and circular body muscles (termed peristalysis), and with the help of chitinous bristles called
setae that project from the body, mobile annelids can move through their environment.
On the outside of the body, besides setae, annelids have a cuticle that is rich in collagen.
Annelids are the most advanced of worms. The digestive system of annelids is complete,
the cells lining the gut termed the gastrodermis. The circulatory system is closed, and includes
dorsal and ventral vessel elements with a series of pumping structures called aortic arches, or
“hearts.” The nervous system features a circumpharyngeal ganglion (“brain”), paired ventral
nerve cords that are connected by ganglia within each segment, and a variety of sense organs.
Respiration occurs through the epidermis and extensions of the epidermis including gills and
parapodia.
Both dioecious and hermaphroditic representatives exist within the phylum, and most
have trochophore larvae. Fertilization may be internal or external. During development, spiral
cleavage is observed.
Introductory Objectives
Objective 1: List the distinctive features that most annelids have.
Objective 2: Explain what metamerism is and give an example.
Objective 3: How does a hydrostatic skeleton allow annelids to move?
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For the Lab Report:
*On the upper, right-hand corner of your lab report, print your name, Biol 212, Lab 6: Phylum
Annelida, and the date you did this lab.
Exercise 6.1: Clade Errantia, Class Polychaeta
Introduction
This is the largest group of annelids, containing about
P
70% of described species. Polychaetes are segmented worms
possessing unique, limb-like structures called parapodia.
Parapodia contain many setae, hence the class name,
“Polychaeta,” which means “many bristles.” This group of
Pa
worms also does not contain clitella; they reproduce mainly
Pr
by shedding their gametes directly into the marine water in
which they live. Polychaetes are found only in the marine
environment, and are especially common in the mud of
P
mudflats.
e
Polychaetes have distinctive and obvious, lateral, footlike structures called parapodia, with numerous setae, that they Fig. 6.1: Head region of a
polychaete, Nereis, showing
use for movement. The complexity of the head region, with its
eversible pharynx, P, and
concentration of sense organs, also serves to distinguish the
jaws. Pr = prostomium; Pe =
polychaetes from the other annelids. The prostomium is the
head segment; it may bear sensory palps and tentacles, and
peristomium; Pa = palps.
eyes. Ventral to the prostomium is the pharynx, which is
sometimes eversible and often bears powerful, chitinous jaws.
The peristomium is the segment immediately surrounding the head; it may also host sensory
tentacles.
Current evidence suggests that all other annelid classes evolved from the class
Polychaeta.
Objectives
Objective 4: Identify a member of the class Polychaeta from either a specimen or photograph.
Objective 5: Identify the following structures on a specimen, photograph or diagram of a
polychaete: parapodia, jaw, pharynx, eyes, prostomium and peristomium.
Materials and Methods
*Preserved polychaetes such as Nereis for observation (not dissection)
-Watch glass
-Dissection microscope, centimeter ruler.
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1. Obtain a dissecting microscope and preserved polychaete worm. Place the polychaete worm
in a watch glass of water.
2. Make a quick overall sketch of the worm as per the For the Lab Report box below; include a
size rule.
For the Lab Report:
1. Write out, “1. Phylum Annelida, class Polychaeta, Genus species, dorsal view.” Make a
quick sketch of the polychaete worm. Using mm or cm, include an accurate size rule, and
indicate the size of the rule to the right of your drawing. No credit for drawings without
accurate size rules. Also, include any notes that might help you to identify the organism on
the lab practical! Have your instructor check and initial your drawings for credit; all drawings
must be completed in lab and signed by your instructor for credit!
3. Examine the polychaete worm under a dissecting microscope. Examine the head region.
Accurately draw the head region. Label the jaw, pharynx, eyes, prostomium and
peristomium, as per the For the Lab Report box below.
For the Lab Report:
2. Write out, “2. Phylum Annelida, class Polychaeta, Genus species, head region.” Accurately
draw the head region, labeling the jaw, pharynx, eyes, prostomium and peristomium. Using
millimeters, include an accurate size rule, and indicate the size of the rule to the right of your
drawing. No credit for drawings without accurate size rules. Also, include any notes that
might help you to identify the organism on the lab practical! Have your instructor check and
initial your drawings for credit; all drawings must be completed in lab and signed by your
instructor for credit!
4. Examine the parapodia. Draw one of the parapodia as accurately as you can, as per the For
the Lab Report box below. Parapodia are an important feature used to determine the species
of a polychaete!
For the Lab Report:
3. Write out, “3. Phylum Annelida, class Polychaeta, Genus species, parapodium.” Accurately
draw a parapodium. Using millimeters, include an accurate size rule, and indicate the size of
the rule to the right of your drawing. No credit for drawings without accurate size rules. Also,
include any notes that might help you to identify the organism on the lab practical! Have
your instructor check and initial your drawings for credit; all drawings must be completed in
lab and signed by your instructor for credit!
For the Lab Report:
Write out thes question then answer it:
4. What are the functions of the parapodia?
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Exercise 6.2: Clade Sedentaria, Class Clitellata, Subclass Oligochaeta
Introduction
The definitive characteristic of the class Clitellata is the presence of a clitellum, a band of
tissue that secretes a cocoon in which fertilized eggs are deposited. Other characteristics include
no parapodia and far fewer setae than the polychaetes, they are nearly all hermaphroditic, with
internal (reciprocal) fertilization. The clitellata do not exhibit a trochophore larva; rather,
juvenile forms look like miniatures of the adult.
The subclass Oligochaeta includes the familiar earthworms, such as Lumbricus
terrestrialis, the night crawler, as well as some aquatic forms. Earthworms average about 7 to 8
cm in length, but may reach 14 inches. Australian earthworm species can attain a length of about
12 feet, with South African species being measured at 22 feet!
Earthworms are beneficial to the soil. One acre of highest-quality soil may host up to
1.75 million worms, with low-quality soil having only 250,000 worms or less. Earthworms take
in and move soil through their gut as they tunnel through the substrate,
processing about 10 pounds of organic matter per year. As they do
this, they aerate the soil, make minerals available to plants, free up
organics by decomposing leaves and molds, and add nitrogen
compounds to the soil.
The head region of a Lumbricus terrestrialis is not a complex
as that of a polychaeta. The first anterior segment is the prostomium,
which overhangs the mouth; the mouth opens in the second segment,
the peristomium. The first through fourth segments make up the head.
The anus opens from the terminal segment.
Moving on down the body of the L. terrestrialis, setae are
located laterally, one row on each side dorsally and one row on each
side ventrally. The setae help the worm to grip the substrate as it
moves through the soil, and to stabilize its position.
Located on the ventral surface of segment 15 on either side are
the male apertures. Running from the male apertures to the
Fig. 6.2: Anterior aspect of
wide, band-like clitellum are the seminal grooves. On the
Lumbricus terrestrialis.
ventral surface of segment 14 are the female apertures, which
are quite a bit smaller than the male apertures and may be
difficult to see. During copulation, the sperm ducts release semen through the male apertures into
the seminal grooves; the semen then travels through the seminal grooves to the paired seminal
receptacles (spermathecal apertures) in segments 9 and 10 of the other worm. After
copulation, the clitellum forms a cocoon that slides up the worm, receiving eggs from the female
apertures, which are openings of the oviducts, and sperm from the seminal receptacles. The
cocoon is deposited in the substrate.
At about the same level as the ventral setae are the openings of the metanephridia, the
nephridiopores.
Lumbricus terrestrialis has a complete digestive system with a closely-associated, closed
circulatory system. The mouth is attached to the wide pharynx, which narrows into the
esophagus, in segments 6 through 13. Immediately before the pharynx is the small, white,
circumpharyngeal ganglion (“brain”) that circles the gut and connects to the ventral nerve cord.
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Running along the dorsal surface of the gut is the
dorsal blood vessel. To either side of the
esophagus are five pairs of aortic arches
(“hearts”), pumping blood from the dorsal blood
vessel to the ventral blood vessel. Of note,
oligochaete blood contains free hemoglobin, not
found in blood cells, which helps it to more
efficiently carry oxygen and turns the blood red;
oligochaete blood cells consist of colorless
amoebocytes. Besides the closed circulatory
system, nutrients, respiratory gases (O2 and CO2)
and wastes are transported by the fluid within the
coelomic cavity (body cavity), the coelomic
fluid, as the worm contracts and relaxes. Note
that the tissue lining the coelomic cavity is called
the peritoneum.
At the distal region (end) of the
esophagus are two to three pairs of calciferous
glands that may be yellow or brown in color;
their function is to gather excess calcium and
carbonate from various food sources, turn it into
CaCO3, and excrete it into the feces. Also in the
region of the esophagus are 3 pairs of large seminal
Fig. 6.3: Dissection of
vesicles.
Lumbricus terrestrialis,
The esophagus empties into a large crop that serves superior view
to store food, and a second wide area, the gizzard, that
grinds food. The
intestine proceeds
from the gizzard
the length of the
body and
terminates at the
anus. Running
virtually the entire
length of the
intestine is the typhlosole. The typhlosole is dorsal
infolding of the intestine that markedly increases its
Fig. 6.4: Lumbricus
absorptive surface area. The principal function of the
terrestralis gut, lateral view.
intestine is digestion and absorption. On the outer surface
of the intestine are yellow to green cells, the chloragogen cells, that store and synthesis glycogen
and fat.
Attached to the ventral surface of the body wall are the three pairs of large seminal
vesicles in the same area as the esophagus. The seminal vesicles, in which sperm are stored and
matured, are attached to the sperm ducts and then the male apertures in segments 9, 11 and 12.
Small, paired testes are found within the seminal vesicles. In segments 9 and 10, the small, round
seminal vesicles are located, their function being to store sperm from copulation. On the floor of
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segment 13, under the last pair of seminal vesicles, are
located the paired ovaries. Posterior to the ovaries, and
draining out of segment 14, are the oviducts.
Excretion in Lumbricus terrestrialis is
accomplished with metanephridia. A ciliated, funnel-like
nephrostome (coelomoduct) opens into and drains the
preceding segment. From the nephrostome, the
metanephridium forms a convoluted tubule that highly
vascularized; fluids that are drained from the preceding
Fig. 6.5: Generalized diagram
segment enter the convoluted tubule and needed substances
of metanephridium.
are selectively reabsorbed back into the blood. The
convoluted tubule opens into an enlarged bladder, that then connects
Fig. 6.6: Lumbricus terrestralis cross section. L
showing metanephridium, on R showing setae
placement.
with the body wall by way of a nephridiopore. Note that the bladder commonly serves as host to
gregarine parasites belonging to the apicomplexa.
The nervous system of Lumbricus terrestrialis begins with the circumpharyngeal
ganglion that surrounds the gut immediately anterior to the pharynx. It is connected to the ventral
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nerve cord. The ventral nerve cord runs along the body wall under the digestive system. It has
ganglia in each segment, with nerves extending out from the ganglia into the body.
Respiration is accomplished through the skin; for this reason, oligochaetes need to live in
moist or aquatic environments. Of note, the epidermis secretes a chitinous outer covering called
the cuticle.
Objectives
Objective 6: Identify a Lumbricus terrestralis as to phylum, class, subclass, genus and species
from a preserved or living specimen, photograph or diagram.
Objective 7: On a preserved or living specimen, photograph or diagram showing the external
anatomy of a Lumbricus terrestrialis, identify the prostomium, mouth, female aperture, male
aperture, seminal groove and clitellum.
Objective 8: On a preserved, photograph or diagram of a Lumbricus terrestrialis dissection,
identify the following: mouth, pharynx, pharyngeal muscles, esophagus, calciferous glands, crop,
gizzard, intestine, anus, cholagogen cells, aortic arches, dorsal blood vessel, coelomic cavity,
peritoneum, cerebral ganglion (circumenteric ganglion), subpharyngeal ganglion, ventral nerve
cord, seminal receptacles, seminal vesicles, metanephridia, nephrostome, septum, convoluted
tubule, bladder and nephridiopore.
Objective 9: On a microscope slide c.s. of a Lumbricus terrestrialis, identify the following:
cuticle, epidermis, circular muscles, longitudinal muscles, coelom (coelemic cavity), peritoneum,
intestine, typhlosole, chloragogen cells, dorsal blood vessel, ventral nerve cord, metanephridium
and setae.
Materials and Methods
*Preserved oligochaetes for dissection
-Dissection pans and tools (needle probes, maul probes, forceps, sharp scalpels or single-edge
razor blades, fine-point scissors, dissection pins)
-Dissection microscope
-Compound microscope
-Microscope slide and coverslip
1. Obtain a preserved earthworm (or one that has been anesthetized in a 7% ethanol solution), a
wax dissection pan, fine-point dissection scissors, single-edge razor blade or scalpel, forceps
and dissection pins.
2. Before you begin your dissection, run your finger along the side of the worm and note the
direction the setae run.
3. Place the earthworm, dorsal-side up on the dissection pan near one of the edges of the pan;
the idea here is that once you have opened the worm up, you should be able to put the pan
under a dissection scope to examine it. Insert one dissection pin just off center through
segment 4 or 5. Stretch the worm out a little and insert the second dissection pin just off
center near the last segment.
4. With a new scalpel or single-edge razor blade (sharpness is needed here), just to the side of
the dark lining running along the dorsum, which is the dorsal blood vessel, cut shallowly into
the body wall. Using fine-point scissors, pulling up as you cut so as to not destroy underlying
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5.
6.
7.
8.
structures, cut the body wall to the head, then cut the body wall to the tail.
Starting at the posterior, gently expose the coelomic cavity by pulling the body wall open on
one side then the other; as you do this, using your needle probe, break the septa between the
segments as these serve to hold the body wall in place. When you have successfully pulled
one side of the body wall open, pin it to keep it open.
At the anterior of the digestive system will be the mouth, then the markedly enlarged
pharynx; coming off of the pharynx will be the numerous dilator muscles used for suction by
the pharynx, torn and made ragged by the dissection. Immediately anterior to the pharynx,
around the mouth, will be the cicumenteric ganglion (cerebral ganglion) or “brain,” which is
white in color. As accurately as you can, draw and label what you see, as per the For the Lab
Report box below.
The pharynx narrows into the esophagus in segments 6 to 13. Identify the seminal vesicles,
attached to the ventral body wall beneath the gut, may partially obscure the esophagus.
Identify the dorsal blood vessel that runs along the dorsal aspect of the gut, and the five pairs
of aortic arches or “hearts” extending down to either side of the esophagus. Identify the
calciferous glands attached to the distal aspect of the esophagus; there should be two or three
pairs of these yellow to brown glands. Also note the coelomic cavity, the cavity in which
these organs are found, as well as the peritoneum, the lining of the coelomic cavity. As
accurately as you can, continue to draw and label what you see, as per the For the Lab Report
box below.
Continuing down from the esophagus, identify the next area of the gut, the crop, and the area
after that, the gizzard, which then continues into the intestine. On the intestine you should see
the chloragogen cells, which should be yellow or green. Continue to draw and label what you
see, as per the For the Lab Report box below.
For the Lab Report:
5. Write out, “5. Phylum Annelida, class Clitellata, subclass Oligochaeta, Lumbricus
terrestrialis, dissection, digestive and circulatory systems.” Trace an overall outline of the
anterior half of your dissection to include the region containing the first part of the intestine.
Identify and accurately draw the mouth, circumenteric ganglion, pharynx, pharyngeal
muscles, esophagus, calciferous glands, crop, gizzard, intestine, anus, cholagogen cells,
aortic arches, dorsal blood vessel, coelomic cavity and peritoneum. Using mm or cm, include
an accurate size rule, and indicate the size of the rule to the right of your drawing. No credit
for drawings without accurate size rules. Also, include any notes that might help you to
identify the organism on the lab practical! Have your instructor check and initial your
drawings for credit; all drawings must be completed in lab and signed by your instructor for
credit!
For the Lab Report:
Write out thes question then answer it:
6. In which direction (anteriorly or posteriorly) do earthworm setae point? Of what advantage is
this to the worm?
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9. With a mall (blunt) probe, lift and push the anterior aspect digestive system to one side; if
you cannot move it easily, you may need to snip the intestine near the anus to free it. Note
how the circumenteric ganglion completely surrounds the mouth, then attaches to the ventral
nerve cord. Identify the three pairs of seminal vesicles in segments 9, 11 and 12. Also
identify the paired, globose seminal receptacles in segments 9 and 10. Posterior to the third
set of seminal vesicles in segment 13, to either side of the ventral nerve cord, will be a pair of
small ovaries. To either side of the ventral body wall you should see metanephridia. As
accurately as you can, draw and label what you see, as per the For the Lab Report box below.
For the Lab Report:
7. Write out, “6. Phylum Annelida, class Clitellata, subclass Oligochaeta, Lumbricus
terrestrialis, dissection, nervous, reproductive and excretory systems.” Trace an overall
outline of the anterior half of your dissection to include the region containing the first part of
the intestine. Outline the digestive system moved to the side. Identify and accurately draw
the cerebral ganglion (circumenteric ganglion), ventral nerve cord, seminal vesicles, seminal
receptacles, ovaries, metanephridia. Using mm or cm, include an accurate size rule, and
indicate the size of the rule to the right of your drawing. No credit for drawings without
accurate size rules. Also, include any notes that might help you to identify the organism on
the lab practical! Have your instructor check and initial your drawings for credit; all drawings
must be completed in lab and signed by your instructor for credit!
10. Posterior to the clitellum, identify the metanephridia to either side of the ventral body wall;
we go here to view the metanephridia as they are largest here. With the fine-point scissors,
snip out a metanephridium, including the septum containing the funnel-shaped nephrostome
that drains the preceding segment and a bit of the body wall containing the nephridiopore.
Mount the preparation on a microscope slide with a drop of water and cover with a coverslip.
Examine under a compound microscope and identify, draw and label the nephrostome,
septum, convoluted tubule, bladder and nephridiopore, as per the For the Lab Report below.
Note that there may be gregarine parasites in the bladder; these are best seen in dissections of
living (anesthetized) worms.
For the Lab Report:
8. Write out, “7. Phylum Annelida, class Clitellata, subclass Oligochaeta, Lumbricus
terrestrialis, dissection, excretory system.” Using a compound microscope, identify and draw
the nephrostome, septum, convoluted tubule, bladder and nephridiopore. Include an accurate
size rule, then include the magnification and indicate the size of the rule to the right of your
drawing. No credit for drawings without accurate size rules. Also, include any notes that
might help you to identify the organism on the lab practical! Have your instructor check and
initial your drawings for credit; all drawings must be completed in lab and signed by your
instructor for credit!
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11. Obtain a commercially-prepared cross section (c.s.) of a Lumbricus terrestrialis. Examine the
cross section under a compound microscope. Identify, draw and label the cuticle, epidermis,
circular muscles, longitudinal muscles, coelom (coelemic cavity), peritoneum, intestine,
typhlosole, chloragogen cells, dorsal blood vessel, ventral nerve cord, metanephridium and
setae, if present, as per the For the Lab Report box below.
For the Lab Report:
9. Write out, “8. Phylum Annelida, class Clitellata, subclass Oligochaeta, Lumbricus
terrestrialis, cross section.” Using a compound microscope, identify and draw the cuticle,
epidermis, circular muscles, longitudinal muscles, coelom (coelemic cavity), peritoneum,
intestine, typhlosole, chloragogen cells, dorsal blood vessel, ventral nerve cord,
metanephridium and setae, if present. Include an accurate size rule, then include the
magnification and indicate the size of the rule to the right of your drawing. No credit for
drawings without accurate size rules. Also, include any notes that might help you to identify
the organism on the lab practical! Have your instructor check and initial your drawings for
credit; all drawings must be completed in lab and signed by your instructor for credit!
Exercise 6.3: Clade Sedentaria, Class Clitellata, Subclass Hirudinea
Introduction
The hirudineans are the leeches. There are over 500 described species of leeches. They
live mostly in freshwater, although a few are marine, and some live on land in warm/hot, moist,
tropical regions. They are united with the oligochaetes by molecular evidence, as well as by the
fact that they possess a clitellum. Hirudineans are segmented, usually with exactly 32 segments,
but generally lack setae. The average size of leeches is 2 to 6 cm or so, with some attaining a
length of over 30 cm! An apomorphic (definitive) characteristic is the presence of anterior and
posterior suckers, with which they use to adhere to the substrate and move sort of like inch
worms. Leeches have a powerful, eversible proboscis complete with three tooth-studded jaws
that are capable of pierce the integument of their hosts; those that feed on blood, release an
anticoagulant, hirudin, into the wound before feeding. They feed by sucking body fluids from
their hosts then dropping off when satiated; some leeches, though are permanent parasites, and
others feed on small invertebrates. The digestion of blood occurs slowly as leeches lack many of
the enzymes needed to digest their food, relying on the digestive activities of symbiotic bacteria
that live in their gut to release nutrients.
Historically, leeches were used to drain “excess blood” from individuals who were ill as
it was thought that some diseases were caused by having too much blood in the body. In modern
medicine, leeches are still being used, this time to remove blood clots resulting from surgery or
injury.
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Objectives
Objective 10: Identify a preserved, living, photograph or diagram of a leech as to phylum, class
and subclass.
Objective 11: Identify the following structures on a preserved, living, photograph or diagram of a
leech: oral sucker, caudal sucker and clitellum.
Materials and Methods
*Preserved leech or plastomount for observation (not dissection)
-Dissection pan
1. Examine a preserved leech. If allowed, remove the preserved leech from its container and
place it on a paper towel in a dissection pan. Draw the leech. Identify, draw and label the oral
sucker, caudal sucker and clitellum, as per the For the Lab Report box below. Return the
leech to its preservative when finished.
For the Lab Report:
10. Write out, “10. Phylum Annelida, class Clitellata, subclass Hirudinea.” Draw the leech and
label the oral and ventral suckers, and clitellum. Using mm or cm, include an accurate size
rule, and indicate the size of the rule to the right of your drawing. No credit for drawings
without accurate size rules. Also, include any notes that might help you to identify the
organism on the lab practical! Have your instructor check and initial your drawings for
credit; all drawings must be completed in lab and signed by your instructor for credit!
~When you’re finished, help clean up!
1. Is your lab bench clean and wiped down with antiseptic solution?
2. Are all materials returned to their proper place?
3. Is the oil immersion objective of your microscope clean?
4. Is the lowest-power objective of your microscope positioned down?
5. Is the power cord draped loosely about one of the oculars?
6. Is your microscope put away?
7. Is all refuse disposed of properly?
8. Is the lab generally in order?
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