294 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the new centrosomes is similar in form and extent to the centroplasra of 

 Figure 54 (Plate 8). But that it is not centroplasm in this case is 

 shown when the stain is nearly all removed, for then the rays may be 

 traced to the central body, — the undifferentiated centrosonie. This is 

 the only case observed in which the wall of the old centrosome persisted 

 in any such form as this. Eggs have been found (Plate 11, Fig. 73) in 

 which the achromatic figure of the second spindle was as far advanced 

 as the one represented in Figure 58 before the first polar cell had 

 formed. 



In my preliminary paper (Smallwood, :01) on Bulla [Haminea] the 

 conditions represented in Figure 59 were described as belonging to the 

 process of fertilization. The egg at that time had a heavy hsematoxylin 

 stain. Since then it has been decolorized and restained in Brazilin ; 

 there are now to be n^cognized deep in the egg seven vesicles, from 

 which numerous rays extend in all directions. The rays all centre at 

 one point. Deutoplasmic spheres are found completely surrounding the 

 vesicles and their rays. The remains of the second maturation spindle 

 are seen at the animal pole of the egg immediately beneath the first 

 polar cell. The chromosomes are small and do not take a heavy stain. 

 No fibrous connection could be traced between them and the rays ex- 

 tending from the vesicles. This stage shows a very unusual variation 

 in the development of the first polar cell and the conditions during the 

 telophase of the second maturation spindle. It has, however, nothing to 

 do with fertilization. 



The maturation changes in Haminea may show considerable variation. 



It is probable, so far as one may judge from the appearances of the egg, 



that in these two cases (Figs. 58, 59) the egg would have segmented. 



It has hitherto been assumed that maturation takes place with a great 



deal of regularity ; but in Haminea there is certainly variability, for not 



only are there two distinct processes in the second maturation phenomena, 



but at some of the stages in each of these processes there is also 



variation. 



(d) Literature and Disaission of Results. 



With the appearance of Boveri's (:01) work on the centrosome, it is 

 probable that there will be no longer such strong opposition to the 

 application of the term "centrosome" to the body which occurs at the 

 centre of the aster, — the body, whatever its size and form may be, in 

 which the primary astral rays terminate. Large centrosomes have not 

 been described in many species of animals, but they seem to be character- 

 istic for Mollusca. The following observers have described large centro- 



