THE FROG 27 



within the mesenteries. The kidneys lie dorsal to the peri- 

 toneum, within the great lymph space between the perito- 

 neum and the dorsal body wall. 



Study the course of the peritoneum in the diagram of a 

 cross-section of the frog's body shown on page 78 of Holmes' 

 Biology of the Frog. Make a similar diagram of a cross- 

 section of the body of a female frog. (This diagram should 

 be about 10 centimeters in diameter.) If your specimen is 

 a male, consult the model showing the internal organs of a 

 female frog, also a preparation of the female reproductive 

 system. 



V. THE DIGESTIVE SYSTEM. 



A. General Anatomy. Review your observations on 

 the anatomy of the digestive system and make an outline 

 drawing (X 3) of the alimentary canal (oesophagus, stom- 

 ach, small and large intestine), showing in addition the 

 liver, gall bladder (bile sac), pancreas and the course of the 

 bile duct. The liver should be turned forward to expose 

 the pancreas, etc. Examine a preparation of the digestive 

 system with the organs arranged in the proper position for 

 sketching, but make the drawing from your own frog. 



B. The Finer Structure of the Alimentary Canal. 



i. Cross-section of the small intestine, (a) Study the 

 section first under low power, then under high power. Ob- 

 serve the shape of the cavity, and the five main layers of the 

 wall, beginning from within: 



(i) The mucosa, or alimentary epithelium. This is 

 thrown into numerous folds. Is there more than one layer 

 of cells? Notice the closely packed nuclei. Observe the 

 goblet cells scattered among the others ; a goblet cell may be 



