ORGANIZATION AM) CELL-LINEAGE OF A.SCIDIAN EGG. 15 



likely, since such parallel chromosomes without any cleft arc found in early stages 

 ((-/. figs. iti. 62), then the first maturation division would separate whole chromo- 

 somes and hence be reducing, while the second would separate half chromosomes 

 and therefore be equational. Only a careful investigation of the manner of origin 

 of these \ -shaped chromosome- would finally solve this problem, and this material 

 is unfavorable for such work. 



Nucleolus. 

 The nucleolus of the germinal vesicle is large and is frequently vacuolated; 



it usually lies eccentrically in the germinal vesicle, though its position hears no 

 constant relation to the polarity of the egg. As is usually the ease, it begins 

 to dissolve at the same time that the nuclear membrane does, and it disap- 

 pears, with great rapidity, so that no trace of it is left by the time that the first 

 maturation figure has reached the metaphase. In this respect it differs materially 

 from the nucleolus of many other eggs, where its solution is so slow that it may 

 not disappear until late in the first maturation division. In this case the solution 

 of the nucleolus is hastened by its breaking up into many small fragments (figs. 

 62, 63, nl.). 



4. Spindle Formation. 

 My observations agree entirely with those of Boveri ( lS'.ldi. .1 ulin dS'JMi. Hill 

 (1895), Castle (1896) and Crampton 1 in showing that there is no trace of a centro- 

 some at either pole of either of the maturation spindles at any time in their his- 

 torv. These results are directly opposed to those of Golski (1809). who found 

 minute centrosomes at the poles of the maturation spindles of Ciona intesti- 

 nalis. Not only are no centrosomes visible in my preparations at the poles of the 

 spindle, but all evidences of astral radiations are also absent. Under these circum- 

 stances the formation of the spindle is of unusual interest. The spindle fibres first 

 appear as lines of granules, which radiate in all directions from the finely granular 

 mass of linin substance which unites the chromosomes in the middle of the nuclear 

 area (fig. 62). These lines of granules are quickly transformed into fibres which 

 run through the linin substance ; these fibres are never parallel at their first appear- 

 ance and frequently radiate in all directions, though they sometimes run in the 

 same general course (figs. 63, 64). As this mitotic figure with the surrounding- 

 nuclear plasm is moved nearer and nearer to the surface of the egg the fibres come 

 to be more nearly parallel, becoming paratangential with the egg surface (fig. 65). 

 In this rearrangement of the fibres they are at first farthesl apart at the ends, so 

 that the spindle has an hour-glass shape (fig. 65). Then certain of these fibres 

 unite at their ends into several groups or bundles, but the fibres which belong to 

 one group at one pole may be associated with different fibres at the opposite pole 

 (fig. CO). There is thus formed a kind of multipolar spindle, closely resembling 

 the mitotic figure present in many plants [cf. Osterhout, 1897: Mottier, 1897: 



1 I am indebted to Dr. Crampton for the privilege of seeing photographs of the beautiful pktes 

 of hi- completed but yet unpublished work on the maturation and fertilization of Molgula. 



