Zool.— Vol. I.] HITTER— DIEMYCTYLUS TOROSUS. 97 



this spine. According to Zeller ('90) the spermatophore 

 of Triton is even more complicated than this. 



Of course my observations cannot be taken as conclu- 

 sive but from the facts at hand it hardly seems possible that 

 there can be any such highly organized structure in the 

 species now under consideration. 



Another circumstance connected with the copulation may 

 be confirmatory of my provisional conclusion about the 

 method of impregnation. In ponds and in quiet places in 

 streams where the water is of considerable depth, mating 

 pairs are almost always seen swimming about, if not at the 

 surface of the water, at least not far below it. I have many 

 times watched these pairs for a considerable period, and it 

 does not appear that they are merely coming to the surface 

 for air or are in transit from one resting place to another, 

 but that it is their custom to swim about while copulating. 

 For the most part the male does the work in swimming, the 

 female remaining quite passive and allowing herself to be 

 carried by her mate ; occasionally, however, I have observed 

 the " weaker sex " to " lend a helping hand," or rather a 

 helping tail, in the labor. One is led to wonder if the in- 

 crease in the width of the tail of the male during the breed- 

 ing season is not for the purpose of increasing its efficiency 

 as a swimming organ, and of thereby enabling him the 

 easier to carry about his mate while copulating. 



Of course if the swimming is continued throughout the en- 

 tire process of fertilization, the sperm mass must reach its 

 destination by some means more direct than that by which 

 the same thing is accomplished in other species. 



I do not wish to be understood to mean that copulating 

 pairs never rest on the bottom; they certainly do, particu- 

 larly when in shallow running water. 



The males of this species are frequently seen carrying 

 on what appears to be quite vigorous contests for the pos- 

 session of the females. 



This I have seen particularly frequently in connection 

 with the swimming pairs. A second male approaches one 

 of these pairs and with movements of unusual energy and 



