316 EDWIN G. CONKLIN 



This introductory account of the aims and chief results of this 

 work will serve perhaps to make more easily intelUgible the fol- 

 lowing detailed account of these experiments. 



3. Material and methods 



The experiments here described were begun ten years ago at the 

 Marine Biological Laboratory at Woods Hole, Massachusetts, 

 and have been continued there almost every summer since. More 

 than one hundred and forty different experiments were per- 

 formed and in every instance the results of these experiments 

 were studied by means of carefully stained and permanently 

 mounted preparations. In the earlier years of this work the eggs 

 in their capsules were centrifuged in a machine driven by hand 

 at such a speed as to make the centrifugal pressure about 2000 

 times gravity; in later years a machine driven by water pressure 

 was used, the centrifugal force being approximately 600 times 

 gravity. There is a slight tendency for eggs to rotate during 

 centrifuging so that the animal pole becomes centripetal and the 

 vegetal pole centrifugal in position, as is shown by the somewhat 

 larger number of eggs in this position than in any other, and yet 

 the viscosity of the fluid in which the eggs are suspended or the 

 pressure of the thin-walled capsules upon them prevents many 

 of the eggs from rotating. Eggs in different stages of develop- 

 ment were centrifuged for various lengths of time. They were 

 then removed from the centrifuge and either fixed at once or 

 left in finger bowls of fresh sea-water for varying lengths of 

 time, as indicated in the description of figures given at the end 

 of this paper. 



In most cases the eggs were fixed, stained and mounted entire 

 in the method described by me in previous papers ('97, '02). 

 These permanent preparations were made soon after the experi- 

 ments were performed and they are still in good condition. 

 Many serial sections also were cut, but in general they are less 

 instructive than whole amounts. All drawings were made with 

 a 3 mm. homogeneous immersion lens with which the finer 

 details of nuclei, centrosomes and cytoplasm can be seen with 

 great distinctness. 



