10 Edmund B. Wilson. 



I shall here give only a very general account of the later his- 

 tory of the two protoplasmic areas, which will require a thorough 

 cytological study for its full elucidation. As the egg, still unfer- 

 tihzed, lies in sea-water, the ectoplasm in the region of the upper 

 disc slowly increases in amount, and in some cases this region 

 shows a faintly radiating appearance around its periphery as If 

 clear hyaloplasm were flowing into it from the surrounding region. 

 I am uncertain whether in this process the original disc itself 

 enlarges or is only surrounded by an accumulation of hyaloplasm 

 — a point of Importance for the comparison with the upper polar 

 ring of the annelid egg that is drawn further on. I shall continue 

 to speak of the ectoplasmic thickening at the top of the egg as the 

 "upper protoplasmic area," but would call attention especially 

 to the fact that the original disc is composed of very dense homo- 

 geneous protoplasm that differs markedly in character from th*: 

 alveolar protoplasm of the ectoplasmic thickening that afterwards 

 extends over the whole upper surface of the egg.^ 



When the germinal vesicle breaks down, the maturatlon-splndle, 

 which is relatively small. Is formed just below this protoplasmic 

 area, rotating into a radial position and moving towards the 

 periphery so that Its outer end lies in or just below It (Fig. ii). 

 In this position it remains, in metaphase, until the egg is fertilized, 

 when the divisions proceed, the polar bodies being successively 

 extruded exactly at the upper pole, at the centre of the upper pro- 

 toplasmic area (which Is now rapidly extending and shows no defi- 

 nite boundary), and hence at the centre of the upper white area 

 (Fig. 4). At this period the protoplasmic area comes Into con- 

 nection by a rather narrow neck of hyaloplasm, in which the spin- 

 dle lies, with the central mass left after the germinal vesicle breaks 

 down. After the polar bodies are formed this connection is sev- 

 ered, and the upper protoplasimc area spreads out still more 



1 The general ectoplasmic layer can in the earlier stages hardly be seen in 

 total preparations, but appears clearly in sections either after staining with 

 haematoxylin and a strong plasma-stain such as Congo red (when it appears 

 clear red) or after borax carmine. It is at first much thinner and less defi- 

 nitely bounded than, for instance, in Rhynchelmis as figured by Vejdovsky,'88 (in 

 the recent paper of Vejdovsky and Mrazek, '03, it is represented as much thinner 

 than in the earlier paper), but later becomes very conspicuous. 



