STUDY OF CELL MECHANICS 471 



acetic, since both of these fluids bring out the achromatic struc- 

 tures. Sections were made at 7/x, the stains used were iron 

 haematoxylin followed by light green. 



In the living egg, very little can be made out on account 

 of the heavy pigmentation. In the following description ob- 

 servations from one set of eggs will be given. There was some 

 variation in the different experiments, of course, but the be- 

 havior of the eggs was essentially the same in all cases. At 

 the time the eggs were transferred to the narcotic, the male 

 pronucleus was already visible as a very small globular body. 

 After the eggs were placed in the solution, it increased very 

 rapidly in size and slowly approached the female pronucleus. 

 In part of the experiments, an ultimate fusion of the pronuclei 

 took place, in others, the male and female elements remained 

 separate. When the fusion did take place, it was very late, 

 for the controls were in the stage when the aster becomes elon- 

 gated into a crescent just before a spindle can be seen. 



After the fusion of the pronuclei there was a rapid increase in 

 the size of the nucleus due to swelling. In the event that a 

 union did not take place, the male element increased greatly 

 in size while the female pronucleus increased only slightly. 

 Then the nuclear wall disappeared and in the egg one could see 

 that the nuclear area showed traces of fibers. This condition fc 

 persisted for a long time. At no period did one find cytoplasmic I 

 radiation. About the time the controls are in the 4-cell stage, ^ 

 the radiations in the nucleus disappear and following this the 

 cytoplasm begins to undergo a labored division during which 

 two or more blastomeres may be separated. Figures Hi to 

 H 4 show camera sketches of such eggs made from in toio mounts. 

 Accompanying this division there was a decided tendency for 

 the pigment to collect in the division plane, showing that there 

 was a flow of the superficial protoplasm, just as there was in 

 monaster eggs. In some few cases the division was permanent. 

 In most eggs, however, after the cleavage furrows had persisted 

 for some time, they would gradually fade out and the egg would 

 resume its normal rounded form. 



