16 SEGMENTATION. 



tion of fresli segments outside the germinal disc and with other 

 facts which I shall mention hereafter, is of great morphological 

 interest as bearing upon the nature and homologies of the 

 food-yolk. It also throws light upon the behaviour and mode 

 of increase of the nuclei. All the nuclei, both those of the 

 segments and those of the yolk, have the peculiar structure I 

 described in the last stage. 



In specimens of this stage I have been able to observe 

 certain points which have an important bearing upon the be- 

 haviour of the nucleus during cell-division. 



Three figures, illustrating the behaviour of the nucleus, as 

 I have seen it in sections of blastoderms hardened in chromic 

 acid, are shewn in PL li. figs. 7a, 7 b and 7c. 



In the place of the nucleus is to be seen a sharply defined 

 figure (Fig. 7 a) stained in the same way as the nucleus 

 or more deeply. It has the shape of two cones placed base 

 to base. From the apex of each cone there diverge to- 

 wards the base a series of excessively fine strioe. At the junc- 

 tion between the two cones is an irregular linear series of small 

 deeply stained granules which form an apparent break between 

 the two. The line of this break is continued very indistinctly 

 beyond the edge of the figure on each side. 



From the apex of each cone there diverge outwards into the 

 protoplasm of the cell a series of indistinct markings. They are 

 rendered obscure by the presence of yolk-spherules, which 

 completely surround the body just described, but which are not 

 arranged with any reference to these markings. These latter 

 striae, diverging from the apex of the cone, are more distinctly 

 seen when the apex points to the observer (Fig. 7 b), than when 

 a side of the cone is in view. 



The striae diverging outwards from the apices of the cones 

 must be carefully distinguished from the striae of the cones 

 themselves. The cones are bodies quite as distinctly dift'er- 

 entiated from the protoplasm of the cell as nuclei, while the 

 striae which diverge from their apices are merely structures in 

 the general protoplasm of the cell. 



In some cells, which contain these bodies, no trace of a com- 

 mencing line of division is visible. In other cases (Fig. 7 c), 

 such a line of division does appear and passes through the 



