No. I.] POLYCHOERUS CAUDATUS. 91 



been fortunate enough to find any stages intermediate between 

 those shown in Figs. 16 and 22, therefore cannot detail the 

 changes which the centrosphere may undergo; but as shown in 

 Fig. 16, the centrospheres have become very much reduced in 

 size, and the centrosomes have entirely disappeared. As shown 

 in Fig. 21, a little more advanced stage, not only do the centro- 

 somes disappear, but the centrospheres are finally reduced to 

 small discs lying as it were on the ring of chromosomes. 

 From this stage on, the cytoplasmic network fades until there 

 is no trace of it left. The chromatic rays which connected 

 the centrospheres with the cytoplasmic network are still left, 

 though much reduced in size, as is shown in this last-men- 

 tioned figure. Fig. 1 7 shows the first polar body immediately 

 after the division has taken place. A small cap of the sub- 

 stance which composed the central mass of the centrosphere 

 rests on the ring of chromosomes, and below this may be seen 

 the remnants of the achromatic fibers. At a later stage the 

 fibers lose their structure and melt together with the stuff 

 forming the cap, and in this mass the chromatin of the chromo- 

 somes collects in scattered particles (Figs. 19 a: and 27). 



The other daughter nucleus of the division lies close beside 

 it (Fig. 19 b), and several times I have seen what I believe to be 

 the first step towards a reorganization. The chromatin in- 

 creases in quantity and breaks up into numerous fine grains, 

 and at the same time the archoplasmic cap divides into two 

 masses, Fig. 18, as if about to form the centrospheres of the 

 new spindle. Fig. 19 a shows a polar body just formed, and b 

 the other daughter product of the first polar spindle. In b the 

 chromatin granules are gathered in what seems to be the 

 region of the future equatorial plate. The achromatic rays 

 are beginning to form, and at each pole clear but small cen- 

 trospheres are formed. Between this stage and one in which 

 there are two polar bodies side by side, and a third body, 

 which without doubt is the female pronucleus, I have found 

 nothing. The polar bodies remain side by side just within the 

 egg membrane (Fig. 27) during several generations of cleavage 

 cells and, as they become less conspicuous with time, probably 

 they are ultimately absorbed. 



