598 AMNIOTA. 



Man) a parepididymis is found on the upper side of the testis. It is 

 usually known as the organ of Giraldes. 



The Miillerian duct forms, as has been stated, the oviduct in the 

 female. The two ducts originally open independently into the cloaca, 

 but in the Mammalia a subsequent modification of this arrangement 

 occurs, which is dealt with in a separate section. In Birds the right 

 oviduct atrophies, a vestige being sometimes left. In the male the 

 Miillerian ducts atrophy more or less completely. 



In most Reptiles and in Birds the atrophy of the Miillerian ducts is com- 

 plete in the male, but in Lacerta and Anguis a rudiment of the anterior 

 part has been detected by Leydig as a convoluted canal. In the Rabbit 

 (Kolliker)' and probably other Mammals the whole of the ducts probably 

 tlisappears, but in some Mammals, e.g. Man, the lower fused ends of the 

 Miillerian ducts give rise to a pocket opening into the urethra, known as 

 tiie uterus masculinus; and in other cases, e.g. the Beaver and the Ass, the 

 rudiments are more considerable, and may be continued into horns homolo- 

 gous with the horns of the uterus (Weber). 



The hydatid of Morgani in the male is supposed (Waldeyer) to repre- 

 sent the abdominal opening of the Fallopian tube in the female, and there- 

 fore to be a renniant of the Miillerian duct. 



Changes in the lotver parts of the urinogenital ducts in the Amniota. 



The genital cord. In the Monodelphia the lower part of the 

 Wolffian ducts becomes enveloped in both sexes in a special cord of 

 tissue, known as the genital cord (fig. 407, gc), within the lower part 

 of which the Miillerian ducts are also enclosed. In the male the 

 Miillerian ducts in this cord atrophy, except at their distal end where 

 they unite to form the uterus masculinus. The Wolffian ducts, after 

 becoming the vasa deferentia, remain for some time enclosed in the 

 common cord, but afterwards separate from each other. The seminal 

 vesicles are outgrowths of the vasa deferentia. 



In the female the Wolffian ducts within the genital cord atrophy, 

 though rudiments of them are for a long time visible or even per- 

 manently persistent. The lower parts of the Miillerian ducts unite to 

 form the vagina and body of the uterus. The junction commences 

 in the middle and extends forwards and backwards ; the stao^e with a 

 median junction being retained permanently in Marsupials. 



The urinogenital sinus and external generative organs. In all 

 the Amniota, there open at first into the common cloaca the ali- 

 mentary canal dorsally, the allantois ventrally, and the Wolffian and 

 Miillerian ducts and ureters laterally. In Reptilia and Aves the 

 embryonic condition is retained. In both groups the allantois serves 

 as an embryonic urinary bladder, but while it atrophies in Aves, its 

 stalk dilates to form a permanent urinary bladder in Reptilia. In 



1 Weber (No. 553) states that a uterus masculinus is present in tlie Rabbit, but 

 his account is by no means satisfactory, and its presence is distinctly denied by 

 Kolliker. 



