796 



FRESH-WATER BIOLOGY 



skeleton of whorled radiating spines. The efferent duct leads 

 to a tube, the vas deferens, which in turn leads to the penis 

 (Fig. 1246 a). 



These forms may also be propagated from unfertilized eggs, i.e., 

 by parthenogenesis. In such cases there may be a sexual genera- 

 tion followed by a number of such parthenogenetic generations. 

 Again, in some forms males have never been discovered, even 

 after as many as 18 years of continuous observation by very carer 



Fig. 1246. Cyprinotus dentate ShsiTpe. (a) Penis, X 210; (b) Efferent or ejaculatory apparatus; (c) Cross- 

 section of same, X 293; (d) Part of a spermatozoon, X 525; (e) Right maxillary palp of male, X 

 158; 00 Left palp of same; (g) Extremity of testicular tube, showing spermatocysts, X 120; (h) Ma- 

 ture spermatocysts, X 120. 



ful observers. Herpetocypris reptans is a good example. Thus 

 some authors distinguish four types of the method of propagation, 

 as follows: 



1. Always sexual as in Notodromas monacha, Cyclocypris laevis, 

 Cypria ophthalmica. 



2. Temporarily parthenogenetic, as in Candona Candida, Cypri- 

 do p sis vidua. 



3. Locally parthenogenetic, as in Cypris incongruens. 



4. Always parthenogenetic, as in Herpetocypris reptans. 



