No. I.] EMBRYOLOGY OF THE ISOPOD CRUSTACEA. 97 



one end a patch of hyaline plasma which segments into large 

 cells extending over the surface of the yolk by the addition of 

 new material added from the yolk. So far as I can understand 

 the brief notice, he believes the mesendoderm to form very 

 much in the manner described by Reinhard. He speaks, how- 

 ever, of nuclei which " naissent spontanement " (!) at the periph- 

 ery of the vitellus, the yolk particles in their neighborhood 

 assuming an altered appearance. In a general way he agrees 

 with Bobretzsky regarding the segmentation, and with Rein- 

 hard in the formation of the germ layers, unfortunately being 

 in error with regard to both processes. In a second paper 

 (Roule, '90) the same author evidently mistakes an ^^'g in a 

 somewhat advanced stage of segmentation for one which has 

 not yet divided. He describes the occurrence of islands of 

 formative plasma at the surface of the yolk, but asserts that 

 only one of them, situated at one pole of the &g%, contains a 

 nucleus ! This nucleated island divides and forms a disc which 

 gradually extends and fuses with the non-nucleated islands, 

 which do not divide until the migration (!) into them of nuclei 

 or particles of nuclear matter from the disc, and the extension 

 of the latter is thus continued. The disc also increases in 

 thickness by the deutoplasm in its vicinity assuming the char- 

 acter of formative plasm, into which nuclei migrate from the 

 disc cells. A truly remarkable series of phenomena ! In this 

 paper, however, he corrects one gross error of his earlier one, 

 denying the spontaneous formation of nuclei, and on the whole 

 comes a little nearer to the truth, though still almost hope- 

 lessly in error. His third paper (Roule, '91) deals with the 

 formation of the germ layers, and he advances the idea that 

 the endoderm, i.e., the liver endoderm, appears in place as the 

 result of a proliferation of the blastoderm cells on each side of 

 the body a short distance behind the head, while the mesoderm 

 arises from the proliferation of the blastoderm cells at various 

 regions, practically, indeed, in every region, a view which is 

 emphasized in later contributions (Roule, '92, '92^). Roule's 

 statements are evidently assumptions based upon imperfect 

 observations, and if proper use had been made of surface views, 

 m.any of them would never have been published. 



