DEVELOPMENT OF PARA VORTEX GEMELLIPARA 477 



The meaning of the j^olk-nuclei of purelj^ cytoplasmc origin is very 

 obscure, and we have at present really no ground for assigning to them 

 any particular function. It can only be said that their appearance 

 coincides in time approximately with the period of greater constructive 

 activity in the cytoplasm but there is no evidence of their direct par- 

 ticipation in the yolk-formation, and we do not know whether ihey 

 are active constructive physiological centers, or merely stores of reserve 

 substances or degeneration products. 



Crampton in 1899 published an account of the 'yolk-matrix' 

 of an Ascidian egg (Molgula). He first noted its appearance 

 in the living primary oocyte as ''one or more small masses of 

 highly refractive granules" lying in the cytoplasm at one side 

 of the nucleus. Later, the granules become more numerous 

 and are closely packed together into a cap-shaped mass which 

 partly encloses the nucleus. Various chemical tests led him 

 to the belief "that the yolk-matrix is an albuminous body of 

 the cytoplasm, but perfectly agrees with the albuminous con- 

 stituents of the nucleus," and that on this ground the yolk- 

 nucleus is either directly derived from the nucleus or is formed 

 under its immediate influence. 



After a time the granules constituting the yolk-matrix sepa- 

 rate, according to Crampton's observation, and spread throughout 

 the cytoplasm in whose interalveolar substance they came to 

 lie. Finally the granules enlarge to form the deutoplasm- 

 spheres. 



In the light of more recent research it would appear that 

 these yolk-nucleus granules are mitochondria, and that Cramp- 

 ton's second alternative as to their origin is the correct one 

 i.e., that they are formed under the influence of the nucleus, 

 rather than directly from nuclear material. 



One of the most prominent types of yolk-nucleus was described 

 in 1898 by van Bambeke for the oocyte of the spider, Pholcus 

 phalangioides. First appearing as a small group of granules 

 near the nucleus, it develops into a definitely outlined, more 

 or less cresentic mass lying in a clear portion of the cytoplasm. 

 Increasing immensely in size the body grows around the nucleus, 

 sometimes adhering to it for a time, but finally reaching the 

 height of its development in the form of a cup within whose 



