Cat: carnivore (mammal)

Rabbit: herbivore (mammal)

Perch: small prey (fish)

Mudpuppy: small invertebrates (amphibian)

Pigeon: seeds, small insects, small amount of veg (bird)

Form and function, comparisons more important than ID

2. Each group of two students will dissect one organism.

Dissection hints:

Cut skin along mid-ventral line from genitals to abdomen.

Cut around neck and paws.

Pull skin off: don’t worry about being gentle.

May want to wrap paws with paper towels and tie with elastics.

Dissect neck and cheeks to view trachea, esophagus and salivary glands.

View dentition on skulls; no need to dissect within mouth to view epiglottis and

glottis. One cat will be on display to show epiglottis and glottis.

For cat, be careful not to destroy circulatory system. Digestive organs can be

pulled out and re-examined next week.

Cut along ventral line from anus to pectoral girdle, then cut up on one side to

just below lateral line.

May want to remove part of operculum and one pectoral fin to get a good view.

Remove breast feathers

Cut across pectoral girdle and down both sides of breast muscle, across in front of cloaca. Lift and remove muscle.

Remove tissue on neck to view esophagus.

Be careful not to destroy circulatory system. Digestive organs can be pulled out and re-examined next week.

Make two incisions, one on each side of the mid-ventral line, from just in front of the pectoral girdle posteriorly through the pelvic girdle to the level of the cloaca.

Be careful not to destroy circulatory system. Be especially careful with the heart when opening the mouth.

1. storage

2. physical breakdown

3. chemical breakdown

4. absorption

#2 must occur before #3: food must be about the consistency of toothpaste.

#3 before #4

Absorption requires surface area.

Digestive tracts differ for different animals.

- In comparisons, consider lifestyles and evolutionary history of animals.

Pancreas marks duodenum. Jejunum, ileum: attaches to large intestine and colon at a T junction with caecum or appendix. Ascending - transverse - descending colon. Rectum exits body.

Four functions of digestive system occur in different places.

e.g.

Role reversal of stomach and intestine with pyloric caecae.

Compare mudpuppy to fish and to mammals. What ancestral and what derived traits can be seen in the digestive tract?

Bird: No physical breakdown in the mouth

Crop - Storage pouch in esophagus

Proventriculus dumps fluid and acid into food just before it enters gizzard.

Gizzard: muscles (almost 1 cm thick) and stones physically break down food (positioned in center of body for flight). Modified for flight, center of gravity

Duodenum loops in V loop with pancreas on loop.

Absorption in intestine

Colic caecae just before rectum - water absorption

Rabbit: cellulose is very hard to break down & therefore more physical breakdown is required.

Rabbit’s digestive tract is much longer than cat’s. Herbivores tend to have longer and more specialized digestive systems. Measure rabbit’s this week, compare to cat’s next week.

Rabbit feeds continuously (small stomach).

Teeth process food (less muscular stomach)

Jejunum much longer than in cat.

Caecum: blind-ended sac with bacterial flora. Tip of caecum is called appendix.

Copraphagy: due to location of caecum after area specialized for absorption. Gives small intestine second chance at absorption of nutrients ; Jerry-rigging evidence of evolutionary processes.

Juveniles consume adult pellets to introduce bacteria

Cat: Buccal cavity: lots of physical breakdown

Large fundus of stomach: storage of large meal. Rabbit, who eats continuously, needs less room for storage.

Cardiac stomach very muscular. Teeth tear, don’t grind: shearing, not chewing

Rabbit has grinding teeth, and therefore needs less muscular stomach.