MUSEUM OF COMPARATIVE ZOOLOGY. 277 



fibrous nature of the structure in question is due to this method of in- 

 vestigation. In tracing the development of the oligoch£etous worm 

 Euaxes, it was discovered that the formation of new cells by segmenta- 

 tion was accompanied by a peculiar modification of the "nucleolus." 

 This is described for the stage in which the embryo consists of only four 

 cells as follows : " The section [Taf IV. Fig. 24] passes through the two 

 small spheres e and c, and one sees that from these two spheres there 

 are beginning to be formed two new smaller ones, in the composition of 

 which the halves of the nucleoli and a small portion of the whole seg- 

 mentation sphere take part. The nucleolus does not appear in the sec- 

 tions as a vesicle in process of division, but exhibits, in the old as also in 

 the newly forming cell, two granular accumulations, which are united to 

 each other by means of fine, granular, but very evident protoplasmic C?) 

 fibres [Strange]." 



There can be no doubt, on examination of the figure, that the so-called 

 granular accumulations are identical with the lateral zones of thicken- 

 ings, and that the Strange uniting them are the interzonal filaments. 

 The former are represented as lying in two parallel planes, appearing 

 consequently in the form of two parallel straight rows of prominent 

 granules ; the latter, as faint lines of much smaller granules, which are 

 parallel or slightly convergent toward the granular accumulations which 

 pertain to the smaller cell. No curvature is shown in these fibres, nor 

 is there any indication of their continuation beyond the two lateral zones. 

 The latter are so far apart that the one belonging to the larger cell lies 

 quite near the centre of the spherical mass of protoplasm which the author 

 leaves one to infer is the nucleus of the larger cell, but which unques- 

 tionably is that portion of yolk protoplasm"^ which is destitute of coarse 

 granules, and which is so often seen to present a radiate appearance. 



Such were the shadowy glimpses that had been caught of the nucleus 

 in its metamorphosis, when, about the beginning of 1874, there appeared, 

 independently of each other, four articles upon representatives of three 

 of the main groups of invertebrates, — coelenterates, worms, and mol- 

 lusks, — each of which devoted considerable attention to the changes in 

 the nucleus before segmentation, and especially to the stellate figures 

 which hitherto had failed to attract much attention or to elicit theoreti- 

 cal notions as to their significance. f 



* Biitschli ('76, p. 398) has already called attention to this as being the first ob- 

 servation on the nuclear spindle, and has also pointed out the incompleteness of 

 Kowalevsky's knowledge of this structure, and its relation to the nucleus. 



t From this point forward the two phenomena, spindle and stellar figures, may 

 be considered together as internal changes of the cell during division. 



