l6 COLD SPRING HARBOR MONOGRAPHS. VII. 



rearing of young from two forms that are found side by side, and 

 that dififer from one another precisely as C. parens differs from 

 C. Americamis, Marsh. 



In companies of Cyclops of the viridis type, C. Americamis 

 may predominate and only a few forms of C. parens may be pres- 

 ent, or C. parens may predominate. Or, as is frequently the case, 

 one of the heterogenous forms may be wholly absent. That 

 heterogeny and polymorphism occur among the Cyclops is well 

 known and fully stated by authors, but in none of the works to 

 which I have had access have any of such forms been either 

 figured or described. 



The first Cyclops of the viridis type described in America was 

 C. inseetus, in 1882, by Dr. Forbes; later in the same year Herrick 

 described C. parens which seems to have agreed very closely with 

 C. inseetus. C. Amerieanns, Marsh, described in 1892, also resem- 

 bles C. inseetus and may be regarded as a synonym for C. inseetus, 

 according to Forbes. 



The close agreement between C. parens and C. Amerieanns in 

 their resemblance to the form Dr. Forbes described as C. inseetus 

 is, it seems to me, explained by the probability that they are hetero- 

 genous forms of the same species. 



Cyelops Brevispinosus, Herrick (Plate VII.). 



General Deseription. — Cyelops brevispinosus is an inhabitant 

 of stagnant pools. It is a well defined Cyclops closely resembling 

 C. Amerieanns, Marsh, and C. parens in its larger outlines. Com- 

 pare Plates v., VI. and VII. It dififers, however, in some details 

 from both of these forms and the differences are relatively con- 

 stant. The fifth foot is usually broader in proportion to its length 

 than in either parens or Americanus. The caudal stylets are not 

 quite so long, and the armature of the swimming feet is charac- 

 teristic and constant in its production of spines in definite places 

 instead of setae. 



The armature of the terminal segments of the swimming feet is 

 as follows : 



