Marsh — North American Species of Cyclops. 1077 



The work of Miss Lehmann (Lehmann '03) proved this in 

 regard to the distinctions between brevispinosus and amerir 

 canus. And yet I am inclined to put much more stress than 

 does Forbes on the varietal distinctions. While we can find 

 connecting forms, if we look for them, yet it is true that col- 

 lections from any locality are apt to contain only one variety 

 in abundance. It is true that one can find the blunt furcal 

 spine of brevispinosus merging by insensible stages into a 

 seta, but it is also true that we can make collections in which 

 practically all the individuals have the blunt spine. These 

 same individuals will have, correlated with the blunt spine, 

 elongated furcal rami, a formula for the spines of the terminal 

 segments of the exopodites of the swimming feet represented 

 by 3, 4, 4, 4, and a spine on the external margin of the 

 terminal segment of the endopodite of the fourth swimming 

 feet. One may find brevispinosus forms with a seta on the ex- 

 ternal margin of the terminal segment of the endopodite of the 

 fourth swimming foot, but this is by no means common, So 

 when one finds parens forms he is not likely to find other forms 

 mingled with it. So with the americanus. There are grades 

 connecting this with the other varieties, but in any given col- 

 lection where americanus is found, nearly all will be typical 

 americanus. 



It is true that the armature of the swimming feet may 

 vary, but variation is not so common, in my experience, as 

 would be inferred from the statements of Forbes. I have even 

 found a form in which the right and left fourth feet in the 

 same individual had a different spinous armature, but this is 

 so unusual, that it may be considered, in all probability, as 

 the result of some mutilation. 



I have sometimes thought that we might well consider these 

 varieties as distinct species, and that the intermediate forms 

 were the result of hybridizing. Whether this is true or not 

 could only be determined by a course of breeding, and it is 

 likely to be a long time before we shall know the pedigrees of 

 the species of Cyclops. Meantime students who must discuss 

 these forms as elements in the plankton, and who, perhaps, 

 have no interest in the taxonomic side of the question, must 



