270 bulletin: museum of comparative zoology. 



3, Figs. 14, 15, 17). In the early stages this cortical layer is well 

 defined, but as the egg develops it becomes less marked, until there is 

 no distinct limit between it and the cytoplasm. 



Astral rays. The astral rays are best studied when stained with hsema- 

 toxylin and differentiated with dilute picric acid. When this method is 

 used, the primary rays can be traced from the region of the poles to the 

 periphery of the egg. The rays end peripherally in a branched mesh- 

 work that is continuous with the common reticulum of the cytoplasm 

 (Phate 3, Fig. 18). These primary rays are easily seen and are arranged 

 quite regularly, like the spokes of a wheel ; along each side of them are 

 arranged a large number of minute bodies (microsomes f). These bodies 

 are not found on the rays in the region immediately outside the cortical 

 layer. They are more abundant in the earlier stages than at any subse- 

 quent time. In between the primary rays are found some of the deuto- 

 plasmic spheres and the coarser structures of the cytoplasm. The 

 secondary rays (Plate 3, Fig. 18) are very much shorter and more 

 numerous. They do not extend far beyond the cortical zone, and do 

 not bear any evidence of being accompanied by such bodies as occur 

 along the primary rays, 



I have been unable to determine in Haminea how the rays are formed 

 in these early stages, but in the formation of the second polar spindle the 

 rays extend out from the region of the centrosome, as in Toxopneustes 

 (Wilson, -.01^). According to Wilson, the rays are paths along which 

 hyaloplasm is moving toward the centre of the aster. Other views have 

 been advanced in regard to the character and origin of the rays. Hill 

 ('95) states that they are formed from a central point and grow outward. 

 Child ('98, p. 394) considers them to be the expression of an activity ; 

 he holds that they come from the cytoplasm, and are mere temporary 

 structures. Mead ('98) argues that the rays are a part of the general 

 reticulum of the cytoplasm. Van I^ame ('99) states that in the case of 

 the first polar spindle the rays from the centrosome at first seem to have 

 little connection with the cytoplasmic reticulum, but that later they 

 branch and grade into the reticulum. Gathy (:00, p. 55) says, in the case 

 of Tubifex, " Les rayons de I'aster sont formes par des cordons de proto- 

 plasme qui s'orientent radialement." Lillie ( :01, p. 231) thinks that 

 the fibres may develop from a common reticulum or foam-structure. 



This is a question that can be satisfactorily settled only upon eggs 

 which permit of being studied in the living as well as in the fixed con- 

 dition. It would seem from Wilson's (:01'') account that the rays must 

 be regarded as thepaths along which particles move toward the centre of 



