202 TRANSPORTATION OF THE GAMETES 



ously through the oviduct and are not retained in the uterus as in the frog 

 (Noble, '31, p. 282). 



b. Other Amphibia 



The transport of the eggs to the site of fertilization in other anuran amphibia 

 presumably is much the same as in the frog, although variations in detail 

 may occur. In the urodeles, however, conditions appear to diverge from the 

 frog pattern considerably. As mentioned previously, fertilization of the eggs 

 of Salamandra atra may occur within the peritoneal cavity before the egg 

 reaches the oviduct, while fertilization in most urodeles occurs internally in 

 the oviduct, either posteriorly or in some cases more anteriorly. In this am- 

 phibian group, the ostium of the oviduct is funnel-shaped and is open, whereas 

 in the frog it is maintained in a constricted condition and opens momentarily 

 as the egg passes through it into the oviduct. (Compare figs. 34, 113.) The 

 open condition of the oviducal ostium in the urodeles suggests that the ostium 

 and anterior part of the oviduct may function as a muscular organ in a manner 

 similar to that of birds and mammals. 



c. Fishes 



Egg transport in the fishes presents a heterogeneous group of procedures. 

 In the cyclostomes the eggs are shed into the peritoneal cavity and are trans- 

 ported caudally on either side of the cloaca to lateral openings of the uro- 

 genital sinus. The eggs pass through these openings into the sinus and through 

 the urogenital papilla to the outside. Contractions of the musculature of the 

 abdominal wall may aid egg transport. 



In most teleost fishes, the contraction of ovarian tissue together with prob- 

 able contractions of the short oviduct is sufficient to expel the eggs to the 

 outside (fig. 28). A somewhat similar condition is found in the bony ganoid 

 fish, Lepisosteus, where the ovary and oviduct are continuous. However, in 

 the closely related bony ganoid, Amia, the eggs are shed into the peritoneal 

 cavity and make their way into an elongated oviduct with a wide funnel- 

 shaped anterior opening and from thence to the outside. A similar condition 

 is found in the cartilaginous ganoid, Acipenser. In the latter two forms, the 

 anatomy of the reproductive ducts in relation to the ovaries suggests that the 

 egg-transport method from the ovary to the ostium of the duct is similar to 

 that found in birds and mammals. Muscular contractions of the oviduct 

 probably propel the egg to the outside where fertilization occurs. This may 

 be true also of the salmon group of fishes, including the trout, where a short, 

 open-mouthed oviduct is present. In the lungfishes (Dipnoi) the anatomy of 

 the female reproductive organs closely simulates that of urodele amphibia. 

 It is probable that egg transport in this group is similar to that of the urodeles, 

 although fertilization in the Dipnoi is external. 



