EARLY DEVELOPMENT OF HYDRA. 1 3 



staining bodies within the cytoplasm of the egg are not alone 

 nuclei, but also nucleoli, or whole cells, and in some cases, the 

 equivalent of two or even three cells, in all of which a certain 

 characteristic change has taken place. 



An examination of Fig. 11, PI. II., and Fig. 14, PI. III., and 

 Fig. 17, PI. III., which are camera drawings of a portion of an 

 egg in which these bodies are very darkly stained, will show that 

 there are three or four different sizes ; there is usually a darkly 

 staining hemisphere while the other shades off almost impercept- 

 ibly into the surrounding cytoplasm, or at most has but a very 

 thin rim of staining material ; that some appear as a mere shell 

 of stained matter with a non-staining interior ; that a very few 

 are exceedingly large when compared with the rest. All of these 

 different kinds are not sharply differentiated but shade into each 

 other as would naturally be expected from the consideration of 

 the processes next to be described. 



The account of the origin of these bodies, which are wrongly 

 called cells, will be given under three headings : (i) Those de- 

 rived from whole nourishing cells, (2) those derived from the 

 nuclei of the nourishing cells, and (3) those derived from the 

 nucleoli of the nourishing cells. 



Pseudo-cells Derived from Whole Cells. 



As previously indicated, the egg grows by tyvo processes, one 

 of which has already been described. The other is by the ap- 

 propriation of the nourishing cells sometimes before any visible 

 change either in size or appearance has taken place. This process 

 is in some cases similar to those which take place when an amoeba 

 engulfs food particles. The cytoplasm of the egg gradually sur- 

 rounds one of the cells and it is finally taken bodily into the egg. 

 Cases of whole cells thus taken into the egg cytoplasm are not 

 rare. Such a one is shown in Fig. 3, PI. I. The cell wall is 

 perfectly distinct and the cell contents differ little in appearance 

 from those of one of the cells outside of the egg. The irregular, 

 dark shading is a peripheral thickening of the protoplasm, as is 

 evidenced by focusing upon different regions of the cell. 



The fact that cells are frequently thus bodily engulfed lends 

 considerable weight to the amoeboid theory of the growth of the 



