102 bulletin: museum of comparative zoology. 



of the inner sphere (centre-some of Boveri), which is evidently analogous 

 to the centrosphere of Scolopendra. He also interprets the central body 

 as the centrosorne, because it serves as the centre of the astral radiations 

 and because it divides to form the ceutres of the next generation of cells. 

 Lillie's observations are very similar to those made independently by 

 MacFarland upon another mollusc (Diaulula), but his interpretation 

 is quite different. Although MacFarland shows that the spindle arises 

 from the substauce of the inner zone, still he calls this structure the 

 centrosorne. Thus the entire spindle is formed directly from the cen- 

 trosorne ! It is of course conceivable that a part of the centrosorne itself 

 should L, r o to form the astral rays, however improbable it may seem ; but 

 to conclude that the whole spindle arises thus seems absurd. 



In Scolopendra the history of the centrosorne and centrosphere 

 absolutely precludes such an interpretation. It is, I believe, impossible 

 that the centrosphere should arise directly from the centrosorne, for the 

 dark central body is at all times visible. Bather the centrosorne seems 

 to exert a formative power upon the archoplasm which causes the great 

 mass of this substance to be converted into fibres at the berdunimr of 

 mitosis. A part, however, is collected about the centrosorne as a reserve 

 supply (centrosphere), and this supply is used in the elongation of the 

 already formed fibres or in the formation of new ones, as occasion 

 demands. 



In the egg of Ascaris Boveri ('83) reported that the centrosorne during 

 metakinesis consists of a rather large sphere containing a central granule. 

 This entire structure is obtained by the elaboration of the centrosorne 

 of the prophase, which at that time is but a simple granule. The cen- 

 triole found in the metaphase would seem to be a direct differentiation 

 product of the surrounding sphere or centrosorne. Quite similar appear- 

 ances were found by the same author in a later study of the egg of 

 Echinus. However, Brauer ('92) found that in the spermatocytes of 

 Ascaris the central granule is present at all stages, and is thus not a deri- 

 vative of the sphere, or centrosorne of Boveri, which surrounds it during 

 , the metaphase. In addition Kostanecki und Siedlecki ('96) announce 

 that in lightly stained preparations of Ascaris the astral rays may be 

 traced to the central granule, and thus, even by Boveri's most important 

 criterion, this body is the centrosorne. Practically' the same conclusions 

 have been reached by other investigators upon material obtained from 

 various sources. In Chaetopterus, Mead ('98) identifies "the minute 

 dark granules in the centres of the asters as centrosomes because they 

 persist and by successive divisions furnish the centrosomes of each 



