114 PEACTICAL ZOOLOGY. 



20. In front of the kidneys are the reproductive organs; 

 the two white oval testes, in the male ; in the female, 

 the ovary, often showing many eggs in different stages 

 of development. The kidneys and reproductive organs 

 send tubes to the cloaca : the tube which conveys the 

 eggs from the ovary to the cloaca is the oviduct. 



21. Remove the heart, cut off the auricles, and look down 

 into the ventricles ; cut across the middle of the ven- 

 tricles, and make a drawing of this cross-section. 



22. Observe the fold of skin extending across the angle 

 between the arm and forearm ; dissect away the skin, 

 and find a membrane within the skin-fold. 



23. Observe the muscles connecting the hinder edge of 

 the breastbone and the pelvis (which were cut through 

 in opening the abdomen); these are the abdominal 

 muscles. How does the bird perform the act of 

 breathing? Compare the bird, snake, frog, and man 

 in their modes of breathing. 



24. Bend the leg up close to the body, to the position of 

 perching; what effect does this bending of the leg 

 have on the toes ? How does the bird stay securely 

 on the perch when asleep? Dissect the leg to find 

 the mechanism by which the toes are clenched as the 

 leg is bent. 



25. Clean away as much as possible of the soft tissues, and 

 keep the skeleton for later study. 



26. Dissect out the tongue, and compare it with the tongue 

 of the snake. The voice is produced in the lower part 

 of the windpipe, instead of in the upper part, as in 

 man. 



