82 BERTRAM G. SMITH 



dlo-piece. Probably the condition observed in the two species 

 represents a late developmental stage of the spermatozoon — the 

 metamorphosis of the spermatid into the spermatozoon is not 

 quite complete. 



The amount of seminal fluid present at one time in the vasa 

 deferentia of a ripe male is very great in proportion to the size 

 of the animal^ — a condition correlated, doubtless, with external 

 fertilization. In one instance 20 cc. of seminal fluid was readily 

 stripped from a single male. 



6. The method of fertilization 



The method of fertilization (external) has already been de- 

 scribed (Smith, '07) ; subsequent observations have supplemented 

 this account only in the fact, discussed later, that a single male 

 may spawn with more than one female. 



The method of external fertilization is well adapted to the nor- 

 mal breeding conditions. The 'nest' of Cryptobranchus consists 

 of a hollow under rocks, a confined space protected from the cur- 

 rent, and filled with very quiet water. As has been shown, the 

 amount of milt that may be discharged at one time by a single 

 male is considerable; in the case of a pair that spawned while 

 being carried in a pail of water, it was sufficient to turn several 

 quarts of water milky white. Such a quantity of sperm set free 

 in the confined space of the nest would become diffused, especi- 

 ally when stirred about by the movements of the animals, so that 

 every egg would be quickly reached and fertilized. As a matter 

 of fact, few unfertilized eggs are found. 



So far as I have been able to learn, this is the only case of exter- 

 nal fertilization recorded for the urodeles. The inconclusive 

 observations of Kerbert ('04) on Cryptobranchus japonicus, 

 and Kunitomo ('10) on Hynobius, suggests to me that external 

 fertilization may take place in these forms. 



In Necturus, from the observations of Kingsbury ('95) it seems 

 certain that internal fertilization takes place. A compound 

 receptaculum seminis or spermatheca is present in the feraale; 

 spermatozoa have been found in these spermathecae during the 



