PLASMA-STRUCTURE IN EGG OF HYDRACTINIA 221 



Eudendrium, among the above forms, has not been re-examined, 

 a brief account of the maturation stgfges occurring in this form 

 will be given here. This section is concerned chiefly with a brief 

 account of the maturation stages in Hydractinia to supplement 

 Smallwood's account which as he states is incomplete because of 

 lack of material. I have been fortunate in finding the stages 

 lacking in his description. 



A. HYDRACTINIA 



1. Nucleus of the growth-period 



As described in the previous section, in the early growth-period 

 the nuclear net is centered in the nucleolus from which it radiates 

 (figs. 2, 3, 4). As the egg grows this radial arrangement is lost, 

 the chromatin assuming a reticular form (figs. 7, 8, 25). While 

 these early stages show the same nuclear structure after preser- 

 vation with any killing fluid, later stages are profoundly modified. 

 When preserved in sublimate-acetic or picro-acetic killing fluids, 

 a coarse, deeply staining, granular reticulum appears in a colorless 

 ground-substance (fig. 12). That this reticulum is a coagulation 

 phenomenon is suggested bj^ comparing this nucleus with those . 

 shown in figures 19, 20, 21 and 23, which are sections of eggs 

 killed in Meves' killing fluid. Here the nuclear net, which has 

 changed into a fine net, stains more Hghtly in basic dyes than 

 after the former fixatives, and lies in a finely granular, homogeneous 

 ground substance which stains hghtly with plasma stains (figs. 

 18, 19, 25). Figures 20 and 28 show a shghtly older stage in 

 which a process of diffusion of the chromatin net, previously 

 begun, has proceeded until there is just a suggestion of the net 

 in the homogeneous ground-substance. This leads directly to 

 the condition shown in figure 21, in which all trace of the net has 

 disappeared and only the ground-substance is left. The question 

 of the method of disappearance of the chromatin will be taken up 

 in detail a little later. The net completely disappears before the 

 egg is one-third grown. The nucleus lies at the center of the egg 

 until near the end of the growth-period when it moves to the free 

 surface of the egg. 



JOURNAL OF MOHPHOLOGY, VOL. 25, NO. 2 



