STUDY OF CELL MECHANICS 465 



spread the phenomena is. 3 Nussbaum ('93) observed that the 

 brownish black pigment found in the entodermal and mesoder- 

 mal cells of young Rana temporaria, tended to collect in a 

 ring around the equator of the cell, and with division this pig- 

 ment sank in and formed a cell plate between the daughter 

 cells. Gardiner ('95) observed substantially the same thing for 

 the cells of Polychaerus and Aphamistoma. Erlanger ('97) ob- 

 served in the nematode egg, a movement of the protoplasm 

 first towards the equator, thence inward and thence toward 

 the asters. More recently Conklin ('02 and '05) has described 

 in detail the vortical movements of the protoplasm in Crepi- 

 dula, and Cynthia. 



,• The intimate connection between the movement of the pig- 

 ment and the changes in surface tension, during the division 

 cycle of monaster eggs, points either to a common cause, or to 

 the one being the effect of the other. And considering the 

 widespread occurrence of the pigment movement in cells of 

 other forms, it is clear that we are not dealing with a force peculiar 

 to the sea urchin egg, but one common to many, perhaps all 

 dividing cells. Any analysis which throws light on the nature 

 of the surface tension changes, or their causes, is a decided 

 advance. 



The first step was to ascertain the cause of the swelling of 

 the ectoplasmic layer. It seemed possible that this was due 

 to some substance diffusing through the egg protoplasm, as 

 Loeb ('95), and Robertson ('08) suggested. If this be true it 

 might be through direct chemical action. I made a few pre- 

 liminary experiments in Naples with this possibility in mind. 

 Dilute solutions of HC1 and NaOH were made in sea water. 

 After the fertilization membrane had been shaken off, the acid 

 was injected against one side of the eggs by means of Barber's 

 apparatus. The ectoplasmic layer increased in thickness. 

 The same results were obtained, however, with the sodium hy- 



3 For a full review of the literature up to 1902 see Conklin's work Karyo- 

 kinesis and Cytokinesis. Since that time I have noted the following works. 

 Fishel ('06) working with Arbacia pustulosa. McClendon ('09) working on 

 Arbacia punctulata. Harvey ('10) working also with this same species. 



