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Ch. 40 - Amphibians
Amphibians are thought to have evolved from
fish. Why?
– Fins into legs, gills into lungs, scales into
skin, stronger bones
Evidence shows to amphibians developed
from a lobe-finned fish (crossopterygians)
Amphibian is Greek for “double life”
The term for land & water is quaiterrestrial
Amphibian Characteristics
1. Ectothermic – cold-blooded
2. Moist skin with no scales
3. Metamorphosis from an aquatic larva stage to an
adult form.
4. Respiration by gills, lungs, &/or skin
5. Eggs fertilized externally
6. Webbed feet (most)
7. 2-chambered heart (larva), 3-chambered heart
(adult)
Ectothermic
States of Dormancy  called Torpor
Why would they undergo torpor?
How can they avoid torpor?
2 types of torpor
1. Hibernation – torpor during the winter.
2. Estivation – torpor during the summer.
Classification
Phylum: Chordata
–Subphylum: Vertebrata
• Class: Amphibia
–Order: Anura “without tails”
–Order: Caudata “visible tails”
–Order: Gymnophiona “without legs”
Gymnophiona
Usually blind, slender-bodies, and
limbless
Burrowing, worm-like amphibians
Seldom seen by humans
Caecilians
Caudata
Elongated bodies, long tails, moist skin
Live in water or moist places
What is Kansas’ state amphibian
–Tiger Salamander
Anura
What is the main difference between frogs
& toads?
How does a toad defend itself?
–Granular glands, inflate their body, bury
themselves
What do toads & frogs feed on?
–Insect  Gardner’s best friend
External Anatomy of a Frog
Nictitating membrane – transparent covering over
the eye (3rd eyelid).
– Allow them to see under water
Tympanic membrane – eardrum for mating season
Eustachian tube – connects the middle ear to the
mouth cavity.
Mucus glands – keep the skin moist for respiration.
Granular glands – secretes toxins
Scientific Name  Rans pipens
Why do frogs have such large eyes?
– This is why they blink when they eat
Do frogs swim as well as a fish?
Why are a frogs legs folded under them?
Why are frogs easily mutated?
Frog’s Internal Anatomy
Have no ribs
It’s tongue is attached to the front of it’s
mouth.
2 vomerine teeth on the roof of their mouth
for holding food.
Maxillary teeth along their upper jaw
Path of Digestion: esophagus, stomach, small
intestine, large intestine, cloaca (the whole
system is called the alimentary canal)
A frog’s esophagus & stomach expand to
allow them to swallow insects.
The food moves from the stomach to the S.I.
By passing through the pyloric sphincter.
Parts of the S.I.
– 1. Duodenum –upper portion
– 2. Ileum- lower portion
Mesentery is a membrane that holds the S.I.
In place.
The liver produces bile to break down
wastes & fats; its stored in the gall
bladder.
The pancreas is next to the stomach.
It enters the S.I. To break down food &
sugars.
Circulatory System
2–chamber as a tadpole, 3-chamber as an
adult
Why would a frog need a 3-chambered
heart?(e.c.)
– On land
3 chambers are: 2 atria & 1 ventricle  Draw
The ventricle receives oxygenated &
deoxygenated blood, which mixed a little.
Respiratory System
What does a tadpole use?
– Gills
What does a frog use?
– Lungs & skin
Pulmonary respiration is through the lungs
Cutaneous respiration is through the skin
Air passes from the throat to the lungs through
the glottis.
Nervous System
Same as the fish; only more developed
Olfactory lobe – which does what?
Cerebrum – which does what?
Cerebellum – which does what?
Optic lobe – which does what?
Medulla oblongata – which does what?
Excretory System
What are the primary excretory organs of
a frog?
–Kidneys
They filter out nitrogenous wastes or urine
The urine travels through the urinary
ducts to the urinary bladder, which
empties out into the cloaca, then out
through the anus.
Reproduction
The male has yellowish white testis that lie in
front of the kidneys
The female have a pair of large lobed ovaries.
The eggs migrate into the oviducts where a
jellylike substance is secreted to protect them.
The eggs are then stored in ovisacs until they
leave the body out the cloacal opening.
External fertilization occurs once a year in
most frogs.
A frog’s croak is produced by air moving
back & forth across the vocal cords.
The male stays attached to the female’s
back during mating this is called
amplexus.
Metamorphosis
Pg. 811
Eggs develop into tadpoles (gills, 2-chambered
heart)  adult (lungs, 3-chambered heart)
As the tadpole develops into an adult hind legs
appear, front legs start to form, & then finally the tail
is reabsorbed into the body.
What is the study of amphibians & reptiles? (e.c.)
– Herpetology