36 COLD SPRING HARBOR MONOGRAPHS. VH. 



Among the Long Island forms a wide range of variation occurs 

 among the members of the viridis type. In C. brevispinosns, for 

 example, the type ranges from the smaller forms of the heteroge- 

 nous form to the largest representative of the group, C. ingensf 



The size of Cyclops seems to be greatly influenced by the habi- 

 tat. Brevispinosns reared in a small aquarium in a dark closet for 

 more than two months were much smaller than were adult forms 

 taken directly from pools where the food and air supply were 

 unrestricted. This variation in size has been observed in almost 

 every abundant species even in a state of nature. 



The study of variation among the Cyclops is greatly complicated 

 not only by the occurrence of sexual precosity (psedogenesis) and 

 by the occurrence of heterogenous forms in certain groups, but 

 also by retardation of metamorphic changes which have super- 

 ficially the appearance of variations, but which disappear in later 

 stages of development when all the metamorphic processes have 

 been completed. 



It is significant, however, that the greatest ranges of variability 

 have been found among those forms that inhabit stagnant water 

 where conditions are most variable and where only plastic forms 

 could live permanently by adjusting themselves to their varying 

 conditions of life. 



Girls' High School, Brooklyn, N. Y., 

 June, 1906. 



