GERM CELLS OF COELENTERATES 33 



Aequorea, Forskalia, and Agalma as beginning only when 

 chromatin passes from the nucleus into the cytoplasm. Jorgen- 

 sen ('10) found similar bodies in the cytoplasm of Sycon sponges 

 at the beginning of growth, Downing ('09) in oogonia of Hydra, 

 and the author ('13 to '18) has noted an apparent correlation 

 between the presence of such cytoplasmic granules and the 

 initiation of the growth processes in the eggs of other Hydrozoa. 

 None of these authors have expressed any thought of these 

 cytoplasmic inclusions acting as indicators of germ-cell or tissue- 

 cell origin, but Hegner ('14), who has collected data from many 

 sources, explains them as germ-cell determinants. 



After growth has once started, it continues rapidly, and re- 

 serve food is stored away for future use. The eggs of some 

 Hydrozoa become filled with large yolk spheres, while in others 

 the yolk is in fine particles so diffused through the cytoplasm as 

 to be scarcely noticeable. There is a great deal of variation in 

 the size attained by these eggs, as the figures and descriptions 

 of the following section will show. 



2. Nuclear growth 



The detailed changes in the nucleus during growth have been 

 described in the papers dealing with particular species; only 

 certain more general relations are here discussed. As the eggs 

 grow, their nuclei also increase, but not in the same ratio. 

 Hertwig's suggestion of a constant ratio between nuclear and 

 cytoplasmic volume is no more supported by the growing eggs of 

 these coelenterates than it has been by other cells investigated 

 by many workers. Jorgensen ('13) has made the claim of a 

 definite relation between the relative size of the nucleus and the 

 mode of nourishment of the egg, basing his claim upon observa- 

 tions of egg cells of a number of different animals. According 

 to this author, eggs nourished by nurse cells or follicle cells, or 

 by the absorption of adjoining ova and oocytes, have very small 

 nuclei; eggs without special nourishing apparatus, but which 

 absorb their food directly, possess relatively large nuclei. In the 

 latter case, he believes, the nucleus of the egg is responsible for its 



