HETEROGENY AND VARIATION IN COPEPODA. 1 67 



the three-jointed condition, and the reduction in the number of 

 spines and setae in the armature of the fourth foot might seem to 

 bear out Herrick's suggestion. 



C. VARICANS. COLD SPRING HARBOR CYCLOPS. 



Fourth Foot. Fourth Foot. 



Outer Ramus. Inner Rannis. Outer Ratnus. Inner Ratmts. 



3 outer spines. I outer seta. 2 outer spines. I outer seta. 



I apical spine. I apical spine. I apical spine. 2 apical spines. 



I apical seta. I apical seta. I apical seta. 



4 inner setse. 4 inner setee. 4 inner setce. 2 inner setae. 



The armature of the Long Island form suggests C. plialeratus, 

 though in the first foot it is not identical. 



I have found three of these forms among a relatively small 

 number of individuals and they agree very closely with one 

 another, the only difference being in a slight variation in the 

 armature of the swimming feet, a spine occasionally appearing in 

 place of a seta. 



Supposing that these individuals represent C. varicans, the 

 Cold Spring Harbor form is very evidently in a later stage of 

 development than the individual figured by Herrick. Any 

 appeal to relative ages as an explanation of differences, requires 

 the supposition that some of the segments of the feet have an 

 adult armature while other segments have not. But there is no 

 reason for supposing that the number of spines and setae in the 

 fourth foot is incident to the breaking up of the rami into three 

 segments instead of two, for the armature of the first foot is not 

 reduced by the presence of the additional joint in the rami. 



SUMMARY. 



The Long Island Cyclops (C. insignisf), having fourteen- 

 jointed antennas, three-jointed rami in the swimming feet, with 

 two-jointed fifth feet and elongate caudal stylets, is a transitional 

 stage in the development of a seventeen-jointed form C. parcus 

 (Herrick ?). The eighteen-jointed antenna is derived from the 

 seventeen-jointed form by division of the seventh segment. 



Out of fifteen individuals taken at random, none of whose 

 antennal segments exceed twelve, five precisely similar individ- 

 uals constitute a group having nine antennal segments, two-jointed 

 rami and two-jointed fifth feet. 



