290 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



clear membrane forms ; also as to the time when the chromosomes pass 

 through the vesicular stage. 



The chromosomes may be grouped into two or more nuclei. In Fig- 

 ure 41 (Plate 7) there are two well-defined nuclei, and at the side of 

 the achromatic figure is the outline of a thin-walled vesicle ; however, 

 no chromosomes could be found in the vicinity of the vesicle in adjacent 

 sections, nor were there any liniu fibres to be observed within or around 

 it. In a second instance the chromatin was found to have assumed the 

 form of two quiescent nuclei before the achromatic figure had begun its 

 peripheral migration, — a fact which would seem to indicate that the 

 formation of more than one quiescent nucleus is independent of the 

 movement of the achromatic figure. 



In the quiescent nucleus the chromosomes remain separate. Before 

 the membrane surrounding them has disappeared and before the spindle 

 rays have come into contact with them, they divide ; but the rod-like 

 form is not assumed before division. It would be impossible to say with 

 confidence that the division is exclusively either longitudinal or trans- 

 verse. In judging whether the division of the chromosomes is lon- 

 gitudinal, one has to be governed by their form. In Haminea the 

 chromosomes are squarish in outline ; but before the division the 

 square form is usually exchanged for an oblong one, and the daughter 

 chromosomes by the transverse division of the oblong chromosomes 

 become small squares. 



When the chromosomes divide (Fig. 48), there appear fine close-set 

 fibres, which gi-ow from the chromosomes in the direction of the two 

 asters till they reach the nuclear membrane (Plate 7, Figs. 47, 48). 

 These fibres continue to grow after the nuclear membrane breaks down 

 (Figs. 49, 54) until they reach the region of the centrosome (Plate 8, 

 Figs. 54, 55). These finer fibres are easily distinguished from the linin 

 fibres in the nucleus (Plate 7, Fig. 48 ; Plate 8, Fig. 55) ; they are not 

 formed from the free linin fibres, but are new outgrowths from the chro- 

 mosomes. 



Astral rays. After the central spindle disappears, the asters are usu- 

 ally located on opposite sides of the nucleus (Plate 11, Fig. 77). There 

 are no rays which are continuous from aster to aster, nor are there at 

 first any connecting the aster to the nucleus (Plate 7, Fig. 48). In the 

 foi'mation of the definitive spindle the cytoplasmic granules in the ter- 

 ritory between the asters and the nucleus arrange themselves into rows, 

 which soon assume the appearance of continuous fibres. These new 

 fibres reach on the one hand to the nuclear membrane, and on the other 



