140 VERTEBRATE ZOOLOGY 



crico-thyroid cartilage, and a pair of small cartilages, the aryte- 

 noids, which guard the opening of the glottis. Cut open a lung and 

 examine its inner texture. Note the large open spaces in it. 

 Exercise 12. Draw a diagram showing the respiratory system. 



The Urogenital System. Observe the cloaca passing to the anus ; 

 observe the rectum and the bladder. Cut a hole in the bladder 

 and probe through it into the cloaca. Probe through the anus into 

 the bladder. 



If the animal is a male, note the large dark-colored penis in the 

 cloaca. Widen the opening of the anus, if necessary, and observe 

 that the penis is a specialized portion of the ventral cloacal wall. 



Free the bladder from its attachments with the surrounding 

 organs, but do not sever its connection with the cloaca. Raise the 

 bladder and observe the two yellow testes, and beside and behind 

 each the black epididymis, which is the terminal portion of the 

 vas deferens. Trace the vas deferens to the cloaca. Lift up the 

 testis with forceps and observe the vasa efferentia, the fine tubes 

 which connect it with the epididymis. 



If the animal is a female, the paired ovaries will be seen in the 

 hinder part of the body cavity, filled with the round yellow ova. 

 A pair of oviducts is present, one on each side of the median line. 

 Each oviduct is a long tube which opens posteriorly into the 

 cloaca ; its posterior end is enlarged, forming the uterus. Its ante- 

 rior end opens by a broad mouth into the body cavity. Straighten 

 out one of the oviducts, cutting the fold of the peritoneum in 

 which it lies. Find its mouth ; if it is hard to find, cut a hole in it 

 and probe forward. In a similar way probe backward into the 

 cloaca. Widen the opening of the cloaca and observe the dark- 

 colored clitoris, which is the homologue of the penis in the male, 

 in the ventral cloacal wall, of which it is a thickening. 

 Exercise 13. Make a semidiagrammatic'clrawing of the genital organs. 



Remove the genital organs. The dark-red kidneys will be ex- 

 posed, lying close to the dorsal body wall. Along the median border 

 of each is an elongated yellow patch, the suprarenal bodies. Trace 

 the short ureter to the cloaca on each side. It is formed by the 

 union of a number of ducts on the ventral surface of the kidney. 



