►STUDIES WITH THE CENTRIFUGE 25 



I wish, here, to acknowledge my indebtedness to Dr. T. H. 

 Morgan, under whose direction the work was done. 



EXPERIMENTS WITH CYCLOPS FIMBRIATUS 

 The normal development 



Cyclops fimbriatus, one of the smaller species of cyclops is 

 easily kept alive in manure cultures, containing protozoa, where 

 it reproduces rapidly in the late winter and early spring. The 

 rate of reproduction at any time of year, however, is influenced 

 by the amount of food material in the culture. 



The egg sacs of the species are comparatively small, contain- 

 ing five to ten opaque blue-gray eggs. Each egg is enclosed in a 

 separate compartment within the sac. The transparent walls 

 separating the eggs are particularly well seen in old sacs from 

 which the nauplii have just escaped. In focusing with the micro- 

 scope on a young egg sac the walls are also visible and are some- 

 times easily confused with the first cleavage plane. The eggs 

 are fertilized in the oviduct of the female. Nauplii hatch from 

 the sac seven or eight days after fertilization, and reach the adult 

 stage and produce egg sacs two weeks later. There is no evidence 

 that the eggs ever develop parthenogenetically. To test the 

 point, however, I isolated the nauplii of a sac when they were 

 only two or three days old and kept them isolated for four weeks. 

 The females did not produce egg sacs during that time, which was 

 two weeks beyond the normal time of maturity. When males 

 were added, egg sacs were produced in the course of two or three 

 days. The development of the eggs is not dependent upon the 

 attachment of the sac to the animal body, for normal nauplii 

 hatch quite as quickly when the sacs are removed and placed in 

 tap water.' 



1 In order to study the living material microscopically the cover slip should be 

 supported just enough to avoid crushing the animal and yet keep it from moving 

 about. For preserving the eggs Carnoy's mixture is an excellent fixative. The 

 adult animals are better preserved with hot sublimate acetic. For a great deal of 

 the work it was necessary to embed isolated egg sacs and for this purpose I adopted 

 the method of wrapping the sac in a small piece of very thin salamander epithe- 

 lium. The egg sac was first stained for several hours in a weak solution of orange 



