A DISCUSSION OF CYCLOPS VIRIDIS JUKI NT.. 293 



for the next three pairs. Anicricanus has three on the first and 

 four on the other three pairs. 



E. F. Byrnes ('09) considers parcits and AmericuHus to be 

 het erogenous * forms of the same species. This she assumes from 

 the fact that the only fundamental difference noted between 

 them is tin- armature of the swimming appendage- and this 

 appear- to !" \ariable, for occasionally one may find an adult 

 ('yilops unmistakably ('. Anicricanus, in which most of the 

 -\\imming feet agree with ('. Americanns in having four spines 

 on tlir terminal -egmcnt- of tin- outer rami, while other- .ire in 

 tin- condition characteristic of ( '. f><irc us, ha\ in- but three -pines 

 on the tcnnin.il -cement- of the rami. 



Neither Byrnes nor Mar-h (*IO have remarked upon the 

 di--imilarity in tin- -hape of the reccpiaculum -eminis of the 

 t\\o forms. S\ -temati-ts working on ( '> i -lopid.e admit that 

 the most constant and < haracteri-tic feature tor a given Species 

 i- the -hape of that organ. It i- remarkable, therefore, that 

 more care is not taken in figuring the -eminal receptacle of 

 de-i ribecl forms. 



In all three varieties tin ^taciilnm consists of a lai 



antcio-nu-dian ])ortion and t\\o narr\\er p'^tcro-\ i-nt ral por- 

 tion-, \\hi< h are carried out laterally a< the -perm dm ts. 



/'iircits i>osscsscs a reci-pt.u-ulum 566 table) \\hiih re-embles 

 that of the Kuropi-an riridis in that the ujiper portion i- concave 

 ant.-riorly. That of AnicricdHiis (see tabl. i- convex. 



\notlit-r point which -eem- tolea\c no room for doubt as to 



the di-tinctne-- of the I u o varieties i- the constant dil'ference in 



their chromosome number. Iha\efound that the somatic chro- 

 mosome number in ( '. .1 nicricanio- i- io \\ hereas in ( '. pure us it i- 6. 



Specimens colli-cted in \\idel\ -eparaied localities, as Toronto, 

 \\'o. ids Mole, and \e\\ \"ork, ha\e thu- far sho\\ n tliis difference 

 in chromo-ome number to be constant for the t\\o varieties. 



A specimen taken from a pure culture of C. parcns showed a 

 variation in the spines of its thoracic limbs, the spine formula 

 being ,,, 4, 4, ,} or 4 (?). A systeniatist would probably consider 



1 Tin- term kctcro^cny is used here to denote the existence of two adult forms 

 \\hi.li represent sue .I'm-rations, both of which are sexually mature, hut 



ii!. -i |>liii|ni;ii-ally unlike. 



