6 GERM -CELL CYCLE IN ANIMALS 



the properties of each and a number of properties 

 pecuhar to itself. No doubt the protoplasm differs 

 in its physical nature in different cells. In the egg 

 of the starfish, Asterias, Kite (1913) has shown that 

 the cytoplasm is a translucent gel of comparatively 

 high viscosity and is only slightly elastic; pieces 

 become spherical when separated from the rest of 

 the egg. Scattered throughout this gel are minute 

 granules (microsomes) about ^ooo mm. in diameter 

 which cannot be entirely freed from the matrix. 

 What appear to be alveoli contain globules which 

 possess many of the optical properties of oil drops; 

 these are suspended in the living gel. The cyto- 

 plasm of the starfish egg is not therefore alveolar in 

 structure as usually stated, but is rather of the 

 nature of a suspension of microsomes and globules 

 in a very viscous gel. The nuclear membrane is a 

 highly translucent, very tough, viscous solid, and 

 not a delicate structure as ordinarily conceived. 

 The nucleolus is a quite rigid, cohesive, granular gel 

 suspended in the sol which makes up the rest of the 

 nuclear material. Dividing male germ cells of cer- 

 tain insects (squash bugs, grasshoppers, and crickets) 

 revealed the fact that the chromosomes are the most 

 highly concentrated and rigid part of the nuclear 

 gel ; that the spindle fibers are elastic, concentrated 

 threads of nuclear gel ; and that the metaphase 

 spindle fibers seem to be continuous with the ends of 

 the chromosomes. 



The ground substance of the nucleus is a sol termed 

 nuclear sap or karyolymph. In the so-called *rest- 



