THE MALE 41 



(ureter) which may be found attached to the lateral margin of the 

 kidney. Within the excretory system the spermatozoa are immotile, 

 due to the slightly acid environment. They are carried passively down 

 the ureter to the slight dilation near the cloaca, known as the seminal 

 vesicle. Within the vesicle the spermatozoa are stored briefly in clus- 

 ters until amplexus and oviposition occur. At oviposition the male 

 ejaculates the spermatozoa into the neutral or slightly alkaline water 

 where they are activated and then are able to fertilize the eggs as they 

 emerge from the cloaca of the female. 



During the normal breeding season amplexus is achieved as the 

 females reach the ponds where the males are emitting their sex calls. 

 During amplexus there are definite muscular ejaculatory movements 

 on the part of the male frog, coinciding with oviposition on the 

 part of the female. Amplexus may be maintained by the male for 

 many days, even with dead females. As soon as the eggs are laid and 

 the male has shed his sperm, he goes through a brief weaving mo- 

 tion of the body and then releases his grip to swim away. The frogs 

 completely neglect the newly laid eggs. 



Accessory Structures 



In the male frog the ureter is not directly connected with the 

 bladder, as it is in higher vertebrates. It is possible that the bladder in 

 the Anura may be an accessory respiratory and hydrating organ, 

 particularly in the toads, where water may be stored during migra- 

 tions onto land. 



The male frog also has a duct, homologous to the oviduct of the 

 female, known as the "rudimentary oviduct" or Miillerian duct. This 

 duct normally has no lumen, and is very much reduced in size so 

 that it may be difficult to locate. There is experimental evidence that 

 this duct may be truly a vestigial oviduct since it responds to ovarian 

 or female sex hormones by enlarging and acquiring a lumen. 



At the anterior end of the testes of some Anura (e.g., toads) there 

 may be found an undeveloped ovary known as Bidder's organ. This 

 structure is said to respond to the removal of the adjacent testis or 

 to the injection of female sex hormones by enlarging to become struc- 

 turally like an ovary. Occasionally isolated ova have been found 

 within the seminiferous tubules of an otherwise normal testis, suggest- 

 ing the similar origin and the fundamental similarity of the testis and 

 the ovary. 



