HETEROGENY AND VARIATION IN COPEPODA. 155 



the pink bodies and the blue eggs, or vice versa, were compara- 

 tively free from the one-celled forms. I believe this fact is 

 important as pointing to the strong probability of a recent moult. 

 Further study revealed the fact that the larger forms had invari- 

 ably seventeen segments in the antennae and that they agreed in 

 all essential details with the species known as C. parcus (Her- 

 rick). 



After formulating data gathered from the study of species- 

 characters in many different individuals from the same locality, I 

 was able to clearly distinguish three groups, in all of which, all 

 the leading species-characteristics of C. parcus (Herrick) were 

 combined with a varying number of segments in the antennae, 

 which, however, all belonged to the same type (Fig. i). 



Group I. comprised individuals with thirteen antennal seg- 

 ments. 



Group II. comprised individuals with fourteen antennal seg- 

 ments. 



Group III. comprised individuals with seventeen antennal 

 ments. 



Nearly all of the Cyclops referred to as covered by protozoa 

 and hence appearing green, belong to Group II. or are inter- 

 mediate between Groups I. and II., and are characterized by an- 

 tennae with fourteen segments either fully formed, or in process 

 of forming. I have studied no less than ten individuals which 

 show clearly that the fourteen-jointed antenna is derived from the 

 thirteen-jointed one, by the division of the tenth segment the 

 fourth from the distal end of the antenna which is divided 

 almost equally into halves by a transverse partition. 



It is always the tenth segment which is dividing at this stage, 

 and in all cases recorded, when the two antennae are not in the 

 same stage of division, it is without exception the left that is in 

 advance of the right, in which division can still be seen in prog- 

 ress, as in Fig. i, B. 



I know of no explanation of the retarded division in the right 

 antenna, and it may be a mere coincidence that all of my ob- 

 servations agree on this point. One Cyclops in which the four- 

 teen segments were perfectly formed in both antennae, proved 

 particularly interesting, for I believe it furnishes positive proof 



