14 BIOLOGICAL LECTURES. 



and while the microsomes may, and probably in many cases do, 

 contribute to the ray, they probably play the part of reserve- 

 material rather than of active elements. 1 



To sum up, the general result indicates that the opinions 

 regarding the aster-formation referred to on page 6 can in a 

 measure be reconciled. In the case of echinoderm-eggs Biitschli 

 and Erlanger correctly describe the aster as involving a radial 

 arrangement of the alveoli, but they have failed to recognize 

 the fibrillae that lie between them, and Boveri is therefore thor- 

 oughly justified in the contention that the astral systems cannot 

 be regarded as merely a radial configuration of the preexisting 

 meshwork. I nevertheless think that Hertwig, Reinke, and 

 myself were right in the contention, which has been made 

 also by many others, that the rays grow by progressive differ- 

 entiation out of the general cytoplasmic meshwork, and that 

 there is no ground, in the echinoderm-egg at least, for the 

 recognition of a specific "archoplasm " or " kinoplasm " from 

 which they arise. 



Finer Structure and Origin of the Meshwork. We may 

 now consider what is, I think, the most suggestive of the ques- 

 tions propounded, namely, that relating to the finer structure 

 and origin of the meshwork. We have thus far distinguished 

 sharply between alveolar spheres, granules, or microsomes, and 

 continuous substance. Morphologically considered, however, 

 there is good reason for the view that all these are but different 

 gradations of one structure. In the first place, a nearly or 

 quite complete series of size-gradations exists between the 

 largest alveoli and the microsomes (Fig. I, b, c). Although 

 most of the alveoli vary but slightly in size from the mean, a 

 little search shows the presence of many smaller ones, and here 

 and there they may seem almost, if not quite, as small as the 

 larger microsomes. In the second place, careful study of the 

 " continuous " substance in life, especially in the crushed proto- 

 plasm, shows that the larger microsomes in turn graduate down 

 to granules so small as to lie near or at the limit of microscopical 

 vision. The "continuous" substance is, in other words, filled 



1 As already pointed out, we cannot assume that the ray is merely an accumula- 

 tion of the continuous substance on account of its different staining capacity. 



