MUSEUM OF COMPARATIVE ZOOLOGY. 351 



area surrounding the spindle figure is interpreted (see also Eberth) as 

 marking the limits of the unmetamorphosed nucleus, and is believed to 

 be filled with nuclear fluid. This area is less common in plant than in 

 animal cells. 



The position of the nuclear [interzonal] filaments at an advanced stage 

 of cell division (that is, whether they converge toward the equator or 

 not) indicates the method by w^hich such division is accomplished, — 

 whether by a constriction, or by the formation of a cell plate simultane- 

 ously through the whole equator of the cell, or by a combination of both 

 methods. In the last case a constriction advances from the periphery, 

 but proceeds only till it reaches the circumference of the spindle, when 

 its work is supplemented by the splitting of an already formed cell plate. 

 The two first-mentioned methods are respectively exemplified, in Mayzel's 

 preparations, by endothelium from the frog's cornea and epithelium from 

 that of the sparrow ; the third method, by Dicyema germs as described 

 by Ed. van Beneden. 



Peremeschko ('78, '78", '78^) gives in preliminary communications 

 the results of his studies on cell division in the case of Triton cristatus 

 in (1.) the epithelium of the body; (2.) star-shaped connective-tissue 

 cells ; (3.) white blood-corpuscles ; and (4.) endothelium of blood capil- 

 laries. 



The process of division is in all cases the same. In the centre of the 



cell appear first small, and then large granules. These change into 



thicker or more slender threads, distributed at first without order. From 



the threads are produced structures which often have a quite regular 



form, — star-shaped, half star-shaped, knotted, etc. These forms are 



, continually changing, and the fibres meantime are now pale, now sharply 



' marked, now longer, now shorter, now finer, now thicker. They exhibit 



no locomotor motion. After these changes they assume a regular cask 



I shape, and become thicker in the middle. (The thickenings do not all lie 



I in one plane.) The fibres divide in these thickenings, and the cask thus 



separates into two similar portions, which at once move apart. Thus the 



! two new nuclei are formed. The contour of the cell then becomes sharper, 



• the protoplasm less transparent, — more compact, as it were, — and a 



furrow, corresponding in position to the space between the new nuclei, 



imakes its appearance, at first on one side and subsequently on the other. 



[The nuclei meanwhile continue for some time to change form, and at 



jlength the constituents of their polar ends melt together. They subse- 



■quently become pale, and finally disappear. 



Flemming ('78) gives in the present paper an extract from a lecture, 



