22 COLD SPRING HARBOR MONOGRAPHS. VII. 



A comparison of this armature with the typical armature of 

 C. hrevispinosus shows that the modified form has a marked ten- 

 dency toward the formation of spines. 



A table of armatures setting forth the variations in a series of 

 eighteen individuals shows seven individuals with one spine and 

 one seta on the apical border of the inner ramus of the third foot, 

 and eleven with tzvo large spines. Of these eleven, three had apical 

 spines on all the rami of the third and fourth feet. This shows a 

 tendency toward a correlated variation in armature, although I 

 have detected no correlated variation in other structures. Should 

 this tendency toward the production of spines become fixed, it 

 would lead eventually to the formation of a new variety. 



Cyclops In gens? (Plate MIL). 



A somewhat rare Cyclops of large size and characteristic appear- 

 ance is occasionally found in connection with C. hrevispinosus. This 

 form is of the inridis type. In color it is pale }ellow (moon- 

 color), with greyish swimmerettes and greyish markings on the 

 borders of the segments. I am inclined to think this may be C. 

 ingens of Herrick, a 'form he describes as "the largest yet encoun- 

 tered in America; it is simply an exaggeration of the last," /. e., 

 Cyclops Americanus, Marsh, "there being no obvious distinctions 

 except in size." 



I have found only the females of this form. They agree with 

 C. hrevispinosus rather than with C. Americanus, Marsh, for they 

 have the spine that is so characteristic of this species in place of 

 the seta of the species described by Professor Marsh. Moreover, 

 they present the two heterogenous forms that are common to C. 

 hrevispinosus. The resemblance between this larger Cyclops and 

 hrevispinosus is further increased by finding the same pale yellow 

 color in some of the individuals of the latter species. It may, there- 

 fore, be doubted whether these larger individuals represent even a 

 distinct variety, so similar are they to hrevispinosus in both of its 

 phases. 



All of these larger Cyclops were taken from larger bodies of 

 water, and their larger size may be the result of their environment, 

 such as a more abundant supply of oxygen and of food. 



