MUSEUM OF COMPARATIVE ZOOLOGY. 317 



tion to the stellate figures, and that they did not occupy the centres 

 of those figures, but lay somewhat nearer each other (p. 108). 



After careful examination the author comes to the conclusion that the 

 large nutritive segment is destitute of a nucleus, and therefore refuses 

 to acknowledge that it is a cell. It is only a detached portion of the 

 nutritive yolk. 



The final paper from Butschli ('76), portions of the substance of 

 which had already been made public in the two preliminary communica- 

 tions that have been passed in review, embraces a wide field of observa- 

 tion, and presents important additional information upon the phenomena 

 connected with cell division. 



In the case of Nephelis (p. 219) the stellate figures about the poles of 

 the spindle receive an attention not accorded them in the preliminary 

 papers. Around each of the ends of the first spindle (Richtungsspindel) 

 is to be seen a clear area (Hof), distinguishable from the remaining 

 yolk mass by its homogeneous condition, from which the yolk granules 

 stretch out radially through the yolk in all directions, — " ein Strahlen- 

 system oder eine Sonne." The clear area possesses no definite boundary 

 toward the granular yolk, bi^t merges gradually into it (p. 216). 



The nucleus of the first segmentation sphere exhibits a distinct, dark 

 envelope (Hiille), and embraces no nucleoli, but instead a clear fluid which 

 is traversed by a number of protoplasmic cords which enclose here and 

 there dark refractive granules, and which are often united into a network. 

 The first segmentation is introduced by an elongation of the yolk and 

 the metamorphosis of the nucleus into a spindle. At each of the oppo- 

 site points af the nucleus which fall in the axis of elongation, there arises 

 in neighboring parts of the yolk a radiation, and at once there begins to 

 appear in the centre of each a clear area of the kind just described. 

 Between these two points the nucleus now begins to undergo a longi- 

 tudinally fibrous differentiation. While this differentiation advances, 

 the still unaltered nuclear remnant continues to exhibit, though less 

 distinctly, its previously described structure, till it at length completely 

 disappears. The volume of such a spindle-shaped metamorphosed nu- 

 cleus is less than that of the original. The change, in Biitschli's opin- 

 ion, can only be explained by supposing that a portion of the fluid of 

 the nucleus escapes during the metamorphosis. 



I pass over points already reviewed in the preliminary papers, and 

 only add that Butschli saw the fibres of the Kernspindel again become 

 thickened and darker in the equator after the beginning of the segmen- 

 tation, and thus form the so-called cell plate of Strasburger (p. 219). 



