THE BREEDING BEHAVIOR OF ANIMALS 



179 



and the cloaca on their way to the exterior. In some species of frogs, 

 the lower end of the ureter in the male may be expanded into a seminal 

 vesicle in which spermatozoa are stored until they are emitted at the time 

 of breeding. 



A comparison of the reproductive systems of male and female frogs 

 reveals that in the male the reproductive organs are more intimately 

 connected with the excretory organs than in the female. In reptiles and 

 birds, the genital system, especially in the male, is mare distinct from 

 the excretory system, though in 

 both of these groups, as in the 

 frogs, both excretory and genital 

 systems discharge into the cloaca. 



In most mammals, the genital 

 and excretory systems open to the 

 exterior through a common open- 

 ing which Is separate from the anal 

 opening. That is, there is no 

 cloaca. In the female, the funnel 

 of the oviduct is close to the ovary 

 but is not connected with it. The 

 oviduct opens into the uterus in 

 which the young are retained and 

 nourished until birth. The form 

 of the uterus differs in the different 

 groups of mammals. That illus- 

 trated in Fig. 148 is common 

 among the carnivores, rodents, and 

 others which bring forth young in 

 litters. The uterus is connected 

 to the exterior by the vagina which 

 is the copulation passage. The 

 urinary bladder, which belongs to 

 the excretory system, is connected 

 to the lower portion of the vagina 

 by means of the urethra. In the 

 male the testes are connected by 

 means of the vasa deferentia (singular, vas deferens) with the urethra, 

 which extends from the urinary bladder through the penis. 



Methods of Ensuring Fertilization. — In chronological order, the first 

 event of the breeding process in bisexual animals is fertilization of the 

 germ cells. From the nature of their reproductive systems it might be 

 expected that this event would occur differently in hermaphroditic 

 animals and those with the sexes separate, for in hermaphrodites self- 



Fig. 148. — ^Urinogenital system of a fe- 

 male mammal having a bicornuate uterus, 

 somewhat schematic, bl, urinary bladder; 

 A;, kidney; od, oviduct; ov, ovary; sug, uri- 

 nogenital sinus; ur, ureter; ut, uterus; ng, 

 vagina; *, position of embryos. {Modified 

 from Wiedersheiyn.) 



