KOFOID: DEVELOPMENT OF LIMAX. 95 



or even clearly present this view, thoxigh he repeatedly calls attention to 

 the lack of a sharp differentiation of the cavity from the protoplasm of 

 the most recent derivative or derivatives of the macromere. The fact that 

 this gradual transition is shown toward two cells, as in his Taf. XII. 

 Figg. 1 i a-(/, and Taf. XIII. Fig. 18 b, militates against the view that the 

 cavity is intracellular. It may well be that the yolk-laden macromere, 

 on account of its different staiuability, is more sharply marked off from 

 the cavity than the protoplasmic micromere ; but is it not possible that 

 the gradual transition of the granular protoplasm of the adjoining cell 

 into the clear space of the cavity is in most, if not all, of the cases figured 

 by Stauffacher due to oblique sections of the limiting membrane ] His 

 figures of the whole egg are made from reconstructions on glass plates, 

 and in them the outlines of the cavities are not distinctly traced. In 

 most cases he has not indicated the planes of the sections which he 

 figures ; these must therefore be inferred from the position of the nuclei. 

 Such inferences, however, lead one irresistibly to the conclusion that the 

 sections must meet the boundary of tlie cavity obliquely wherever its 

 outline appears indistinct ; e. g. Taf. XII. Figg. 14 a—g; Taf. XIII. Figg. 

 18 a and b. On the other hand, sections which appear to sti'ike the 

 cavity perpendicularly, as in Taf. XII. Figg. 15 a and 6, 16 a and h, and 

 11 a, all show a much more distinctly marked separation of the proto- 

 plasm of the cells from the cavity, and in some cases this demarcation is 

 as definite on the side of the most recent microraei'e as it is upon that 

 of the macromere. In case this explanation should prove valid, we shall 

 have in Cyclas, as in Limax, an intercellular cavity appearing at the 

 two-cell stage, and recurring in the later stages of cleavage. 



I cannot agree with Stauffacher's view that this primitive " heller 

 Rauui " has nothing whatever to do with the true cleavage cavity. It 

 is not established even by the facts found by him in Cyclas ; much less 

 by a comparison with other forms presenting a similar phenomenon. 

 His observations are confined to killed, preserved, and hardened material 

 of very limited amount. He had in some cases not more than one series 

 of sections of each cleavage stage ; of the three-cell stage seven series, of 

 the four-cell stage six series. He has not been able to examine the eggs 

 in the living state, or in whole preparations. Thus he has been deprived 

 of most valuable assistance in determining the origin, definite bounda- 

 ries, successive phases, ultimate fate, and relationships of this " heller 

 Raum," whose claim to the title of cleavage cavity he so summarily 

 dismisses. The " unumstosslich Beweis " which he brings forward to 

 support the view he advances is, that the " heller Eaum " finally dis- 



