218 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



give a correct idea of this " Schaumwerk " structure, if one imagines the 

 yolk granules many times smaller and the protoplasmic films much more 

 slender than in the egg of Distaplia as represented by Davidoff. 



The ventral hemisphere also is filled with yolk granules, but here the 

 protoplasmic packing between them is more abundant and less uniformly 

 distributed. It is most conspicuous at the surface, where it forms a 

 thin layer nearly free from yolk granules spreading over almost the 

 whole hemisphere. Within this layer it fades away gradually, but 

 often, as in the case figured (Fig. 1), again becomes prominent at a little 

 deeper level as a series of irregular blotches among the yolk granules ; 

 then it once more grows fainter toward the centre of the egg, attaining 

 the condition described for the dorsal hemisphere. 



The presence of a spermatozoon cannot be detected in the eggs of this 

 lot. In those of Series B, lot 3, however, its influence is clearly visible. 

 (See Figs. 2 and 4.) About fifteen minutes is estimated to have 

 elapsed between the stage just discussed and the one here presented. 

 At this stage we see in the ventral hemisphere, at some point just 

 beneath the surface, a spherical region entirely free from yolk granules. 

 (See Fig. 2.) Its central portion is occupied by a finely granular sub- 

 stance, which stains in hfematoxylin an intense blue, shading off some- 

 what gradually into the more faintly and lightly colored protoplasm 

 occupying the outer portion of the area and continuous with the sim- 

 ilarly stained films of the Schaumwerk. At one point the yolk-free re- 

 gion extends out to the surface of the egg. This probably represents the 

 place of entrance of the spermatozoon, which we have reason to believe 

 produces the clear area. The deeply staining substance at the centre of 

 this area is the male archoplasm or attraction sphere. It is undoubtedly 

 similar in nature, as it is in optical appearance, to the darkly stained 

 substance seen at the deep end of the maturation spindle in Figure 1, and 

 which may therefore be called the female archoplasm. The male pro- 

 nucleus cannot be made out in the egg a portion of which is shown in 

 Figure 2. In other eggs of the same lot, however, it can be clearly seen ; 

 for example, in Figure 4, which represents a stage a little more advanced 

 than the one seen in Figure 2. The area free from yolk is seen in Figure 4 

 to have enlarged somewhat; the attractive influence of the archoplasm 

 at its centre has manifestly been extended over the greater portion of the 

 hemisphere in which it lies. This fact is indicated diagrammatically by 

 the dotted lines in the figure. They are meant simply to indicate that 

 those films of the protoplasmic Schaumwerk which run radially with 

 reference to the attraction sphere have become thicker and more promi- 



