MUSEUM OF COMPARATIVE ZOOLOGY. 267 



are differentiated into rods, which are soon drawn together by a contrac- 

 tion of the Zwischensubstanz, lose their sharp outline, become irregularly 

 curved, and so joined together that there results an indefinite network of 

 coarser distinct, and of finer blurred fibres. This network is the typical form 

 of the highest differentiation of the nucleus, which may vary in the fineness 

 of its fibres and the closeness of its meshes in cells from different embryonic 

 stages. 



Often cells are to be found in which, by the side of one or two existing 

 nuclei, two, three, or even four new nuclei may arise ; and their development 

 may be traced. ( !) New nuclei may arise by a process of formative differentia- 

 tion from the Dotterpliittchen. Neither cell nor nucleus has always the same 

 signification. A nucleus may later attain the dignity of a cell. 



The studies of Torok can hardly be considered as convincing proof that the 

 prevailing histological notions are altogether out of joint. Few, I suspect, will 

 be inclined to admit so prominent and active a role for the Dotterplattchen, 

 even in those objects which form the basis of Torok's studies, to say nothing 

 of the cases where such " Formelemente " (e. g. Cucullanus) are wanting. It 

 is not easy to understand why the sudden rearrangement of the yolk elements 

 into a radial position is necessarily to be referred to the yolk particles them- 

 selves as the efficient living substance, rather than to the homogeneous matrix 

 in which they lie. The proof of this assumed explanation appears to be en- 

 tirely wanting. 



That the changes described — certainly the " Stabchen-Faden " — are phases 

 of nuclear division can hardly be doubted. Fig. 11 is particularly strik- 

 ing in comparison with the amphiasters of segmentation, and many of the 

 other figures are readily comparable with stages of division which have been 

 so exquisitely figured by Flemming in his last paper ('78^). 



In a recent communication, Eimer ('77) defends his previous papers from 

 the charge of representing artificially produced conditions of the nucleus. The 

 " clear area " receives the name of " hyaloid," and the " circle of granules " 

 separating it from the peripheral portions of the nucleus is now called 

 " shell of granules " (Kornchenschale), as expressing more accurately the 

 spatial distribution of the granules. Stimulated to renewed studies of nuclei 

 by the work of Heitzmann and Flemming, Eimer finds occasion to extend 

 somewhat the nature of his earlier conclusions respecting the structure of 

 nuclei, inasmuch as he finds that very generally the granules of his " Kornchen- 

 schale " are connected, each by a delicate radiating filament which traverses the 

 " hyaloid," with the nucleolus, a clear indication of this arrangement having 

 been already figured by him ('73, Taf. VIII. Fig. 82. h) in his Beroe studies. 

 Further than this, Eimer corroborates the view that the nucleus consists of a 

 hyaline '' Grundsubstanz " traversed by protoplasmic filaments. Outside the 

 " Kornchenschale " these filaments form a network of narrow meshes, which 

 has usually been mistaken for a granular structure, but within that " shell " 

 only the radial fibres are met with. The latter — and of course the " granules " 

 — are nearly constant in number, so that about nine are in the field of vision 



