388 



THE AMERICAN NATURALIST 



[Vol. XLI 



number of spermatophores that must be depositerl. "With Amhly- 

 stoma pundatum, on account of the very large innnber of sperma- 

 tophores, there is the probabiHty of a simpler mode of behavior, 

 and the spermatophores may be found lar<jely by chance. The 



Axolotl there is evidently no clasping- of the female by the male, 



"Vhv result of the ex])erimental work on the vitality of the seminal 

 fluid in water indicates that the s])ermatophore is not necessarily 

 taken uj) by the female immediately after it is deposited; probably 

 it is capable of effecting fertilization after exposure to the water for 



On account of the shortness of the breeding season, the sperma- 

 tozoa can be retained in the cloaca of the female for only a few 

 days at most, before fertili.-.ation is effected. The position with 

 respect to the spermatophores, of the earlier eggs fouiul, .suggests 

 that in some cases the eggs are deposited inunediately after the 

 spermatophores are picked up. 



The extreme flexibility of the sperm is doubtless correlated with 

 the process of internal fertilization. In Cryptobranchus, in which 

 fertilization is external (Smith '07), the egg envelopes nuist be 

 penetrated after a brief exposure to the hardening elVect of the 

 water, and a much more riuid spermatozoon is nM|uir(Ml. 



In the evolution of terrestrial from a.|natie vert<4.rate \Wv, a 

 transition from external to internal fertilization takes place. 

 External fertilization is not ada[)ted to terrestrial conditions, 

 hence in the land-living vertebrates it occurs only in some of the 

 forms that revert to the water during the breeding season — r. e. in 

 the Amphibia. Internal fertilization is an ada{)tation to terres- 

 trial life in the sense that it is a condition aiU(>ce(lent to that life, 

 not a result brought about by it; it may occur in purely aquatic 

 vertebrates, as in the Elasmobranchs and a few Teleosts. Internal 

 fertilization by means of spermatophores is a method still adapted 

 to aquatic rather than to terrestrial conditions. It is a method 

 intermediate between external fertilization on the one hand aiul 

 internal fertilization withont spermat()])li()res on th«' other. \'iewe(l 

 in the light of tli(> linhil. of the ]w^hvv vertel.rale.. the oecnrrence 



