156 Harry Lewis Wieman. 



insects, and earthworms. In all these cases the action of differen- 

 tial stains indicates that the substance of the yolk nucleus is 

 nearly related to chromatin, as I found to be the fact with the 

 nutritive material in the egg of Leptinotarsa. The close prox- 

 imity of the yolk nucleus to the germinal vesicle has led many 

 workers to regard it as derived from the chromatin. Possibly 

 when more complete data are at hand, it may be shown that in 

 these forms, as in Leptinotarsa, the yolk nucleus is nothing more 

 nor less than a nutritive stream that has its origin in cells out- 

 side of the ovum; that is, in the follicle or nurse cells, as the case 

 may be. 



It is rather interesting that the chromatin and the granules of 

 the nutritive stream should show similar reactions toward the 

 basic dyes. The granules are used in the formation of the yolk, 

 and the product resulting from this transformation takes the 

 acid stain. In the development of the embryo there is a rever- 

 sal of this process. At fertilization the germ nuclei unite in the 

 center of the egg, and the cleavage nuclei become scattered about 

 in the yolk. These nuclei, which take the basic stain as intensely 

 as the nutritive granules or the chromatin, then migrate in part 

 to the pheripheral layer where they form the blastoderm, and in 

 part, remain in the yolk as the yolk nuclei. Through the activity 

 of the latter, the yolk is converted into a form which can be assim- 

 ilated by the growing embryo. Thus the agencies which are con- 

 cerned with the conversion of the inert yolk into living proto- 

 plasm, the yolk nuclei, are somewhat similar in chemical make-up 

 to the material from which the yolk is elaborated, the granules of 

 the food stream. The entire process bears considerable resem- 

 blance to a reversible chemical reaction. 



It is well known from the work of Loeb ('02) and Mathews ('07) 

 that the eggs of the starfish, Asterias Forhesii, if allowed to mature 

 in sea water in the presence of oxygen soon die, unless fertilized. 

 Mathews has shown that the early death of the egg after matura- 

 tion occurs only when free oxygen is present : from which it is con- 

 cluded that death is brought about by the oxidation of the cyto- 

 plasm. Furthermore, this takes place much more rapidly after 

 the contents of the germinal vesicle have been discharged into the 



