THE LOWER VERTEBRATA. 



155 



but appear simply as a yellowish patch on the ventral 

 surface of each kidney (figs. 77 and 78). 



18. Uro-genital Organs: Female (fig. 77). In the 

 female, the ovaries, instead of being the tiny bodies seen 

 in the rabbit occupy an enormous space in the coalom : 

 this is due partly to the far greater number of eggs laid, 

 and partly to the much greater size of each egg a rabbit's 

 ovum being only -^-^ 

 inch, while a frog's is 

 j^j- inch in diameter. 

 The ovaries occupy 

 their primitive posi- 

 tion, nearer the 

 middle line than the 

 kidneys. The ovi- 

 ducts are relatively 

 much longer than in 

 the rabbit, being 

 very much coiled and 

 extending forwards 

 to the lungs, close to 

 which they open into 

 the cffilom. The first 

 part of the oviduct 

 is thin and narrow ; 

 the longest, middle 

 part is much coiled, 

 thick - walled, and 

 secretes an albu- 

 minous substance with which each egg is coated as it 

 passes down, and which has the property of absorbing 

 water when placed in it and so swelling up enormously ; 

 the final portion is broad and thin- walled, and opens, on 

 either side, into the cloaca. 



The kidneys of the female are reddish-brown organs that 

 do not project into the coalom, but lie in the subvertebral 

 lymph-space, being covered by peritoneum on their ventral 

 surface only. From the outer border of each comes oft' a 



Fig. 77. UROQKNITAL ORGANS OF FF.MALE FROG. 



The left ovary, kidney, etc., and most of the left 

 oviduct, are omitted. (After Howes, altered.) 



