MATUI{ATION OF OVUM IX ECHINUS KSCULEiSTTUS. 187 



tion of fixation and the manner of staining, presents different 

 appearances. 'J^his accounts for the different forms under 

 which the body has appeared. It stains best with iron 

 heematoxylin, and destains concentrically. When destaining 

 has been carried far, it shows as a discoidal area surrounded 

 by a clear halo, and has a very fine alveolar structure. This 

 is the form in which I have observed it in all mj osmic acid 

 preparations, except that I do not see the halo, and when 

 counterstained with rubin it has a red colour, which in- 

 definitely fades away into the bluish-grey astral rays and 

 spindle fibres. This rounded body, as division proceeds, 

 becomes enlarged, then lens-shaped, and ultimately flattens 

 into a plate which lies along the side of the nucleus. In 

 polar view this is dumbbell-shaped ; the enlarged ends are 

 the daughter eentrosomes which become surrounded with new 

 radiations. In the maturation stages my preparations are 

 not numerous enough to enable me to follow in detail the 

 behaviour of the eentrosomes, and I have not been fortunate 

 enough to see the division of the body in the first maturation 

 spindle. The centrosome of Boveri corresponds to the 

 centrosphere of Wilson. In another set of preparations less 

 destained, Boveri described the centrosome as a smaller body, 

 showing in its centre a darkly staining particle, the ceutriole, 

 which corresponds to Wilson's centrosome. This, as division 

 proceeds, divides into two, and goes through the usually 

 described evolutions. In picro-acetic and sublimo-acctic 

 preparations I have seen such a centriole, but have been un- 

 able to trace its division. Again, when destaining has been 

 stopped early the whole centroplasm is black. This 1 have 

 also seen in picro-acetic and sublimo-acetic material. The 

 rays, according to Boveri, stop at the margin of his centro- 

 some, and do not enter it so as to be inserted into the centriole. 

 This seems to be the case, and in my cleavage preparations 

 fixed with Lindsay Johnstone's fluid the central reticular 

 body is sometimes seen to have completely dropped out, so 

 that the astral rays are seen to end abruptly, leaving an 

 absolutely round empty space occupied in the other eggs by 



