THE STRUCTURE OF PROTOPLASM. 13 



erally they may often be seen to run out into rows of granules 

 like beads on a string. Van Beneden, .who has been followed 

 by many later writers, was inclined to regard the rays as essen- 

 tially rows of microsomes strung together by a homogeneous 

 clear substance, i.e., by the continuous substance, and I was 

 led to the same conclusion in the case of sea-urchin eggs. A 

 study of the asters in Ophiitra throws doubt upon this conclu- 



FIG. 4. Section of sea-urchin egg (Toxopneustes), \\ minutes after entrance of the sperma- 

 tozoon, showing sperm-nucleus, middle piece, and aster (about 2000 diameters). 



sion, for it is here certain that the larger and deeply staining 

 microsomes do not build up the ray, but are quite irregularly 

 scattered along its course. The rays here mainly arise, I believe, 

 in, and at the expense of, the continuous substance, and the 

 linear arrangement of the microsomes is incidental to the dif- 

 ferentiation of this substance along a definite tract which more 

 or less involves the microsomes as it progresses. This conclu- 

 sion probably also applies to other forms. The material active 

 in the ray-formation appears to be the continuous substance, 



