RELATIONSHIPS AMONG CYCLOPS. 4! 



During the study of the metamorphosis of Cyclops, which i> 

 about to be published, I have had the opportunity of obscrx in- 

 many details of structure throughout their entire- history ,md 

 have been able to compare these details in one Cyclops with 

 corresponding details in another form. 



Two of the forms used in the study of the metamorphosis were 

 C. signatus, var. tenuicornis and C. signatus var. coronatus. 

 In C. tenuicornis the armature of the distal segment of the inner 

 ramus of the fourth swimming feet is very characteristic. The 

 inner margin of this segment carries two seta 1 , the more distal of 

 which is extremely small or may even be wholly wanting in 

 which case the site of the seta is marked be a notch in the chitin. 



In C. coronatus this distal seta is fully developed agreeing in 

 size with all the other seta." in the armature. 



While the fourth swimming feet are among the later structures 

 to develop during the metamorphosis, they may be said to un- 

 dergo four stages in development. During the first stage they 

 are too immature to even suggest their later characteristics. 

 During the second stage' the appendages are well formed though 

 only one-jointed; Nevertheless, the terminal armature is present 

 and the setae on the inner margins of the inner ramus already 

 show their adult characteristics. In the young of C. signatus 

 var. tenuicornis the distal seta is reduced as in the parent form 

 from which the young is derived. When the next molt occurs 

 the foot becomes two-jointed but the distal armature of the distal 

 segments remains unchanged. After the next molt the appen- 

 dages become three-jointed as in the adult. Still the distal 

 armature is unchanged and though the Cyclops molts again before 

 acquiring its adult condition no further changes occur in the 

 armature of the swimming feet. New setae and spines may be 

 added as new segments are formed but each seta retains its 

 original characteristic throughout the metamorphosis. 



These studies were made on the broods of females that were 

 isolated while they were carrying their appended egg-masses. 



Each female was transferred to a separate aquarium usually 

 to a small petri dish. The water was carefully filtered and micro- 

 scopic algae were added after careful examination under the 

 microscope showed them to be entirely free from any forms that 

 might contaminate the results of the experiments. 



