22 LABORATORY STUDIES IN ZOOLOGY 



buried in the substance of the kidney is a narrow yellowish band, 

 the adrenal gland, where there is produced a secretion of impor- 

 tance to the life of the organism. Usually closely associated 

 with the anterior ends of the kidneys is a pair of bright yellow 

 finger-like tufts of flattened processes, the fat bodies. These 

 vary much in size at different seasons of the year. 



The reproductive system consists of the sex organs, or gonads, 

 in which the sex elements are lodged, and ducts extending to the 

 cloaca. 



In the male frog the gonads are termed the testes (singular, 

 testis). They may be seen as small, yellow, bean-shaped organs 

 located at the ventral surface of the kidneys. A number of 

 slender ducts, the vasa efferentia, may be made out in the mesen- 

 tery between each testis and the inner border of the corresponding 

 kidney. Spermatozoa (the male reproductive elements) pass 

 through these ducts into the tubules of the kidneys and thence 

 to the cloaca by way of the ureters. A tube conducting the 

 spermatozoa from the testis toward the exterior is called a vas 

 deferens. It will be seen that in the frog the ureter serves both 

 as ureter and vas deferens. In many species, and especially is 

 this true of the leopard frog {Rana pipiens), the male possesses a 

 vestigial oviduct which appears as a wavy white tube on each 

 side, laterad of the ureters. 



It will be noted by those who have female frogs that the ovaries 

 lie in the same relative position as do the testes of the male but 

 vary considerably in size and shape according to the season of 

 the year. The most conspicuous organs in the celom of a mature 

 female in the spring are the ovaries, bearing great numbers of 

 ova. The ovaries bear no such relation to the kidneys as do the 

 testes in the male but, as already mentioned, shed their eggs 

 into the body cavity whence they make their way to the openings 

 of the oviducts, which they follow to the exterior. The funnel- 

 shaped mouth of an oviduct may be visible close to the outer 

 side of the root of the lung of the same side. The opening of the 

 oviduct through the dorsal wall of the cloaca should be identified. 

 Unhke the male, the female possesses genital ducts independent 

 of those of the urinary organs. 



After locating and studying all organs and structures described 

 above, label those shown on the plate and add any which may 

 not be represented. The reproductive system on the right side 

 only need be shown. 



