202 THE CELL 



observers. The half-spindles, described by van Beneden and 

 Boveri, consist of a portion of the protoplasmic radiation figure 

 proceeding from the poles, namely, all those fibrils which are 

 situated in the equator around the nuclear segments. The true 

 spindle lies in the centre of these protoplasmic fibrils and nuclear 

 segments. Hermann, to distinguish it from van Beneden's 

 spindle, has given it the name of central spindle. The prefix 

 " central," however, appears to me to be quite superfluous ; for 

 one thing, it is better to decide to limit the name of spindle once 

 for all to this portion of the nuclear figure, and to give, if 

 necessary, some other name to the protoplasmic polar rays, which 

 are connected with the nuclear segments, and which are described 

 by van Beneden and Boveri as half-spindles ; indeed, the name 

 spindle is not suitable to them. 



Another moot point is the derivation of the spindle fibrils. 

 Many investigators are inclined to trace them back to that 

 protoplasm, which forced its way in between the nuclein threads 

 when the nuclear membrane was dissolved (Strasburger VI. 72 ; 

 Hermann VI. 29, etc.). I have already advocated, and am still 

 inclined to hold the view, that, with the exception of the polar 

 radiations, which belong to the protoplasmic body of the cell, the 

 various structural portions of the nuclear figure are derived from 

 the various substances in the resting nucleus. I consider that the 

 substance of the spindle and of the connecting fibrils is derived 

 from the linin framework. This view is supported also by Flem- 

 ming, and to some extent by the micro-chemical investigations of 

 Zacharias. However, the most important facts in its favour 

 appear to me to be the following : 



In many unicellular organisms the nuclei, during certain stages 

 of division, remain separated from the protoplasm by a delicate 

 membrane ; this occurs in Euglypha (Schewiakoff VI. 65b), and in 

 the nuclear divisions of Giliata and Actinosphceria (Rich. Hertwig, 

 VI. 82, 83). Under these conditions there can be no doubt but 

 that the spindle threads have sprang from the achromatin portion 

 of the nucleus itself. Similar cases are occasionally met with in 

 the animal kingdom as well. In some molluscs (Pterotrachea, P/n/l- 

 lirhoe), as Fol (VI. 19a) and I myself (VI. 30a) have observed, the 

 polar spindle, as long as the nuclear membrane remains, is situated 

 in the interior of the germinal vesicle (Fig. 97 A, B), which, in 

 this case, is of small size. The assumption that, under these cir- 

 cumstances, protoplasm has made its way into the nuclear space 



