BYRNES: CYCLOPS OF FRESH WATER. 2 1 



It has been repeatedl}- noticed that the proximal spine on the 

 terminal joint of the outer ramus of C. brevispinosus is usually 

 smaller than the more distal ones (Fig. 8, Plate VII.). This 

 smaller size probably means a more recent formation, but I have 

 been unable to find any direct proof of this. I have not seen the 

 origin of this spine. 



Failing to obtain proof of the descent of the "parcus-stage" from 

 C. brevispinosus, fertile females of the "parcus-stage" were isolated 

 and from these individuals were reared C. brevispinosus with the 

 three outer spines. All of these young that were observed were 

 males. Whether or not they produce only males 1 am not prepared 

 to say. 



This experiment entirely establishes the true relation between the 

 two forms, however, and illustrates a striking case of heterogeny. 



Just wdiat relation these two heterogenous forms bear to one 

 another in the line of descent has not been fully determined. But 

 of their close relationship no doubt remains. They are both abun- 

 dant, similar in appearance and both attain to the later stages of 

 sexual maturity side l)y side, but maintain a marked difference in 

 armature that might almost seem to indicate a distinct difference 

 in the species of the two forms. 



Variations i'l Cyclops Ih-C7'ispinosus. — A marked variation in 

 C. brez ispinosus is seen in certain individuals that show a modifi- 

 cation in the armature of the outer ramus of the fourth swimming 

 feet. The usual armature of the inner margin of the outer ramus 

 is three seta; (Fig. 2, Plate A II.). In the modified form one or two 

 of these seta? become distinct spines, so that the entire armature is 

 as follows : 



Foot No. 



Ramus, Outer or Inner. 



O 



Outer Spines 



Apical Spines H 



Apical Setie ' "2 



Inner Seta; , 3 



11 

 1 

 1 

 3 



II 



III 



IV 



'seta, ^uneciual. ^2 spines+l seta. 



