EXPERIMENTS IN BREEDING AS A MEANS OF 

 DETERMINING SOME RELATIONSHIPS AMONG 



CYCLOPS. 



ESTHER F. BYRNES, PH.U. 



Two of the largest as well as the most common forms of 

 Cyclops are Cyclops signatus, var. coronatus (C. fuscus J urine) 

 and Cyclops signatus var. tenuicornis 1 (C. albidus J urine). 



Herrick, in his key to the Cyclops ("Copepoda, Cladocera 

 and Ostracoda of Minnesota ") says of these two forms: "Of the 

 identity of the two varieties which have so long been recognized 

 as distinct species (C. tenuicornis and C. coronatus) the writer 

 has little doubt. The developmental history has been traced 

 sufficiently to settle this point." 



C. tenuicornis and C. coronatus are easily distinguishable by 

 the naked eye when adult, and on closer observation they are 

 found to possess several different and very constant character- 

 istics. 



C. tenuicornis is generally smaller than C. coronatus; the chit in 

 is less deeply pigmented and less hairy; the second segment of 

 the antennule is relatively longer than the corresponding segment 

 in C. coronatus as is also the basal joint of the fifth foot. 



C. coronatus is larger than C. tenuicornis; the chitin is more 

 strongly colored and more hairy; the second joint ot the four- 

 jointed antennule is always relatively short as is also the ba>.il 

 joint of the fifth foot. When adult, the- female carries her dark 

 egg-masses closely applied to the abdomen. In ('. tenuicornis 

 the egg-masses are divaricate. 



I have attempted to decide the question i>\ any possible- identity 

 of these two forms by studies in inheritance. 



1 C. signatus annulicornis seems to be synonymous with C. signatus lenuicornis. 

 Fig. 2, Plate XXXIII.. Copepoda, Cladocera and Ostracoda of Minnesota, shows 

 the fourth swimming foot of C. lenuicornis with two well-l'm m<-il <t-\-.i\- mi (In- 

 inner margin of the distal segment of the inner ramus. The mai.ui"^ tlu-niselvcs 

 are also strongly hairy. These characteristics are constant in all stages ol ' 

 signatits. var. coronatus, but I have not noted them in ( '. li-intimriii^ (iiniuilii crw/.\ i. 



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