CONTRIBUTIONS TO THE STUDY OF CELL 

 MECHANICS 



I. SPIRAL ASTERS 



THEOPHILUS S. PAINTER 



{Instructor in the Sheffield Scientific School) 

 From the Osborn Zoological Laboratory, Yale University 



SEVEN TEXT FIGURES AND TWO PLATES 



While making an experimental study of sea urchin eggs in 

 Naples, during the spring of 1914, it was the good fortune of the 

 author to observe one case of a 'spiral aster.' The egg in which 

 this was seen had previously been treated with a dilute solution 

 of phenyl urethane shortly after f-ertilization, and had subse- 

 quently been washed free of the narcotic. 



Since taking up a cytological study of the sea urchin material, 

 collected at Naples, a number of asters with bent or twisted rays 

 have been observed to occur at a definite period in the develop- 

 ment of certain monaster eggs. That these stages are not due 

 to faulty preservation is proved from several considerations. 

 First, the phenomenon has been observed and followed in the 

 living egg. Second, it appears, as we shall see, at definite phases 

 in the development of certain monaster eggs in two separate 

 series of material preserved at different times. Third, one may 

 trace the history of the asters from the time when the first bend- 

 ing appears until it finally disappears. 



The facts, in the case of the sea urchin, pointed so clearly to 

 one interpretation only, that I took up a review of the more im- 

 portant papers where spiral asters have been recorded in order 

 to see in how far the explanation arrived at from the study of 

 Strongylocentrotus would be applicable to the observations of 

 other workers dealing with widely different forms. The result 

 has been so satisfactory that it seems worth while to describe 

 in detail the phenomena observed in the eggs of Strongylocen- 



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