No. I.] GERM-LAYERS IN CLEPSINE. 135 



an early stage of the embryo, before the germ-bands have 

 reached the equator of the egg, and the illustrations for the 

 earlier phases described (Figs. 1-5) are drawn from eggs of C. 

 complanata, obtained at Naples. 



Figure i represents a surface view of the q.^%, with the germ- 

 bands in an equatorial position, before they have united at the 

 cephalic end. The white patches (enp) seen in the yolk, be- 

 low the germ-bands, are nucleated masses of finely granular 

 protoplasm, to which I have given the name entoplasts. The 

 existence of such bodies was entirely overlooked by Hoffmann 

 in his first paper ; but in his second paper he describes them 

 as " Protoplasmaflecke " and devotes considerable space to re- 

 futing my interpretation of them. Nusbaum (No. 8, p. 2) 

 carefully translates Hoffmann's description, as if it were some- 

 thing original, using "tlotsprotoplasmiqties" as the equivalent 

 of Hoffmann's term. 



Sections of the egg (Figs. 2-5) show that many of the ento- 

 plasts have not yet reached a peripheral position. In a 

 sagittal section of the head (Fig. 4) we see scattered entoplasts 

 (^enp) in the yolk, and external to them some large entoderm 

 cells {ert). Some of these cells are only faintly or imperfectly 

 circumscribed by boundary lines, representing transitional 

 phases between the entoplast and the clearly defined entoderm 

 cell. The differentiation of the entoplasts is going on more 

 rapidly in this region than elsewhere, and it is here that they 

 first assume an epithelial character. Another sagittal section 

 of the same Qgg, nearer the median plane, is seen in Fig. 3. 

 Here the same large entoderm cells are seen beneath the head 

 (<:/), and a few neighboring entoplasts, not yet delimited, against 

 the yolk. This one section shows fourteen entoplasts, only 

 three of which could have been seen from the surface. The 

 rest lie beneath the cephalic lobe (c/) and around the meso- 

 blast X, which is here nearer the anterior than the posterior 

 end of the egg. In the transverse section (Fig. 2) fewer ento- 

 plasts are seen, — four in a, three in c, and one in b. The pro- 

 toplasm surrounding the two nuclei at the upper angle of c is 

 continuous with the ectoblast, which raises the question whether 

 contributions to the latter have continued up to so late a stage. 

 I am not able to decide the question, but I am inclined to think 

 that the macromeres cease to proliferate ectoblastic elements 



