326 W. WESCHE ON MALE ROTIFERS. 



large spermatheca tapers down to the end of the foot, which 

 practically forms the penis. Several of the specimens seen were 

 rather granular in appearance, but one was exquisitely hyaline, 

 and I was able very clearly to see the spermatozoa moving about 

 inside the spermatheca, and to obtain a measurement of a 

 spermatozoon, namely, YTS"y ' — ^^/"" 



Size ^/ - ^J/ = 90/. - 70/x. 



Habitat, pond at Neasden on private ground, February 7th 

 and 8th, 1902. 



This form is interesting as it enables us to make some 

 comparisons with the males of allied genera. It may not be 

 superfluous to state that Triarthra longiseta ? is one of those highly 

 modified Rotifers which have the faculty of jerking themselves 

 through the water by means of more or less lengthy spines. It 

 is impossible to generalise or to formulate a law from the small 

 amount of information available, but, judging by Polyarthra and 

 Fedalion, it seems a rule that where the female is highly 

 elaborated and provided with leaping spines and setae, the 

 structure of the male is simple and has a tendency towards 

 degeneration. 



The comparatively unimportant part played by the male in 

 rotatorial life is shown by the fact that he is quite unpro\'ided 

 with protective appliances, or with any of those numberless 

 contrivances so common in insects and known as secondary 

 sexual characters. 



It is evident from the following facts, namely, that some males 

 are supplied with digestive organs, that others have rudiments of 

 glands and stomach, while others, like the animal just described, 

 have lost all traces of such structures, that we have a process of 

 degeneration going on under our eyes, and that possibly all 

 males may ultimately degrade to the low stage represented by the 

 male of Polyarthra, an amorphous body, ciliated at two extremities 

 and provided with no structure except a spermatheca. Going 

 even further, the male may disappear altogether, which would 

 explain the fact that no male has been found in the Philodinadae. 



