28 GEORGINA B. SPOONER 



sitic copepods, also, the direction of the first cleavage plane is 

 influenced by compression of the eggs in the egg strings as well 

 as when the eggs are compressed by artificial means. 



Development of the egg after centrifuging 



For the following experiments a hand centrifuge was used, and 

 the animals were revolved for 1^ minutes (9000 rev.) at a radius 

 of 7 cm. The adult animals, though thrown to the bottom of 

 the tube and held there, recover in two or three seconds and are 

 apparently uninjured. 



The materials of unsegmented eggs, which have been centri- 

 fuged for 1^^ minutes (9000 rev.) at a radius of 7 cm. are divided 

 into three layers (fig. 8). At the centripetal pole is a cap which is 

 white by reflected light under the microscope and gray-green by 

 transmitted light. The rest of the centripetal hemisphere con- 

 tains a clear band of protoplasm, and the centrifugal pole is blue- 

 gray in appearance because of the densely packed yolk spheres. 

 The white cap turns black with osmic and is partially dissolved 

 in alcohol. Hence it is probably chiefly oil as in other eggs. 



A centrifuged egg, sectioned and stained with Delafield's 

 haematoxylin and orange G, is shown in fig. 2. The yolk spheres, 

 crowded together in one hemisphere, take the yellow stain. In 

 a well centrifuged egg there are no purple granules between the 

 yolk spheres as there are normally. The rest of the egg with the 

 exception of the aster stains with haematoxylin. The asters are 

 yellow. The green cap is only distinguishable by the vacuoles 

 left where the oil has been dissolved out in the alcohol. The mi- 

 totic figure, whether it be resting nucleus or cleavage spindle-, lies 

 in the purple hemisphere near the cap and, in the case of the 

 spindle, parallel to the cap. 



When a living egg has been centrifuged (just after the seg- 

 mentation nucleus has enlarged), and the separation into layers 

 is very distinct, movement is visible among the small green spheres 

 of the cap. At first it is not different from Brownian movement. 

 But as the spindle forms, clusters of the spheres sway in one direc- 

 tion or another, indicating the flowing movements in the sur- 



