130 PRINCIPLED OF ANIMAL HIOLOGY 



entia. At the other end the vas deferens is connected to an evertible 

 copulating organ, the cirrus or penis, which hes, when not everted, within 

 a penial pouch. The principal female organs are the bilobed ovary, 

 the so-called vitelline glands, nterus, and the ducts which connect these 

 organs with each other and with the exterior. Of these ducts the copula- 

 tion passage, or vagina, opens to the exterior beside the cirrus through a 

 common genital chamber. The vagina extends inward and backward 

 and then expands into a receptaculum seminis in which the sperms are 

 stored, and thence proceeds backward to join the oviduct which takes its 

 origin from the mid-piece of the bilobed ovary. From the junction of 

 the oviduct and vagina, a continuation of the oviduct which serves as a 

 fertilization passage discharges into the ootype. The ootype receives also 

 the vitelline duct which may be traced to the vitelline glands, so called 

 because they were once believed to furnish the yolk for the eggs. Into 

 the ootype the oviduct discharges fertilized ova while the vitelline duct 

 discharges cells from the vitelline glands. In the ootype each ovum and a 

 group of vitelUne cells are converted into what is commonly called the 

 egg, which is covered with membranes. These eggs are conducted through 

 a uterine passage to the uterus where they and their developing embryos 

 are stored. The uterus is at first a straight tube without branches, but 

 as the proglottis (segment of the tapeworm) becomes older the uterine 

 walls put out hollow lateral branches which become filled with eggs. In 

 this tapeworm there is no definite opening of the uterus to the exterior 

 but finally the ventral wall of the proglottis splits lengthwise opening up 

 the uterus and discharging the eggs. 



Urinogenital Systems. — In vertebrate animals the reproductive and 

 excretory systems are intimately connected and together they comprise 

 the urinogenital system. The excretory system of the frog has already 

 been described. In both sexes of the frog the gonads develop ventrally 

 to the kidneys and here they hang suspended in loops of peritoneum. 

 This relation is most plainly seen in the male and in young females 

 whose ovaries have not yet become voluminous. 



Lying dorsally to the ovaries in the female frog and extending into 

 both ends of the body cavity are coils of the oviduct (Fig. 97). Each 

 duct takes its origin in a ciliated funnel which lies just dorsal to the heart 

 and at the extreme anterior end of the coelomic cavity. The posterior 

 end of each oviduct is transformed into a thin-walled distensible bag, the 

 uterus, which is connected by means of a narrow passage with the cloaca, 

 in the same region as the opening of the ureter. The walls of the uterus 

 and the ureter become united side by side in their lower courses but their 

 cavities remain distinct. Eggs are released into the body cavity by 

 ruptures in the peritoneum covering the ovaries. They are carried for- 

 ward to the funnels of the oviducts by the currents caused by general 

 body movements, assisted by pressure of the fore arms of the clasping 



