482 J. DUESBP^RG 



one more solid part (reticulum, interalveolar substance, mitome, 

 spongioplasm, kinoplasm). This second part, viscid and elastic, 

 may be stretched and distorted by centrifuging, but it is capable 

 of recovering its normal form afterward. It forms a framework 

 running through the cell and connecting the nucleus and centro- 

 some or centrosphere, with a peripheral layer surrounding the 

 entire egg. This framework is the seat of the polarity and 

 pattern of organization of the cell; it holds the cell-organs, es- 

 pecially the centrosphere and the nucleus, in a definite relation 

 to each other and to the cell-axis — it prevents the complete 

 stratification of cell-substances into sharply marked zones ac- 

 cording to their specific weights. The substance of this frame- 

 work is probably identical with the 'ground-substance' of Lillie, 

 though in Crepidula it constitutes a relatively small part of the 

 cell-contents and, in Conklin's opinion, does have "a filar, 

 reticular or alveolar structure." 



The ch'ef and real interest of Conklin's observations lies, in 

 my opinion, in the fact that they might afford an explanation 

 of the behavior of centrifuged eggs in further development. 

 They show the existence in the ground-substance of the egg, 

 of a special, firm architecture, which determines, or helps to 

 determine the polarity. ^ Whether, however, from these ob- 

 servations on the egg-cell, general conclusions may be drawn, is 

 another question: the egg is not of a simple, but of a compli- 

 cated cytoplasmic structure. It must not be inferred that I 

 intend to deny the existence of zones of different consistence, 

 of a special repartition of gels and sols in other cells; their exist- 

 ence can be deduced from the study of fixed material and is cor- 

 roborated by the experiments of microdissection. But the same 

 experiments show that the consistence of the different parts of 

 the cell-body changes during the life of the cell, and the study 

 of fixed material teaches that a centrosphere, for instance, may 

 not exist, as such, in a young cell, and yet may differentiate 

 later, — a view which is supported by the occasional incor- 



^ Concerning connections between asters and egg-periphery, see Van Beneden 

 and Neyt ('87). 



