600 GRIFFIN. [Vol. XV. 



the daughter-chromosomes are seen to be united by wavy and 

 very granular interzonal fibers (PL XXXIII, Fig. 42), most 

 of which later disintegrate (cf. Wilson, '95), though after the 

 cleavage-furrow is complete, a few of these are still present 

 and converge to several black granules in the furrow or to a 

 single small black cell-plate (PI. XXXIII, Fig. 46). 



No sooner is the equatorial plate fairly established than the 

 cloudy area, with its contained centrosomes, commences to 

 migrate toward the outer periphery of the centrosphere where 

 the cloudy area, having grown much less distinct, finally fades 

 out entirely (PI. XXXIII, Fig. 41). The centrosomes now 

 diverge, and by mid-anaphase set up a minute amphiaster super- 

 imposed upon the crown of astral rays (PL XXXIII, Fig. 43). 

 Aside from a slight elongation, it persists in this condition 

 during the rest of the anaphase, the formation and fusion of 

 the vesicles, and throughout the persistence of the reconsti- 

 tuted daughter-nucleus (PL XXXIII, Figs. 43-46). The cen- 

 trosomes, by continued divergence, finally reach opposite poles 

 of this nucleus, and the prophase of the second cleavage is thus 

 initiated. Every step in this whole process can easily be fol- 

 lowed out in detail, and there can be no question that the 

 centrosomes persist throughout. 



The initiation of a new and independent astral system under 

 the apparent stimulus of the centrosome, while the persisting 

 rays of the old still converge to a point previously occupied by 

 the centrosome, is a fact noted by other investigators, although 

 it has not, I believe, received the attention it deserves. Besides 

 instances figured by Boveri ('90), MacFarland ('97), and others, 

 the most striking case is perhaps that of the trout, as figured by 

 Henneguy ('91). Here, within the old centrosphere, a minute 

 aster is developed about each of the diverging daughter-centro- 

 somes. Outside the long astral rays of the old system still 

 converge toward the center of the former centrosphere. While 

 he does not emphasize the point in the text, a comparison of 

 his figures clearly brings out the migration of the daughter- 

 centrosomes to the outer periphery, exactly as in Thalassema. 

 Such facts as the above, I believe, lend the strongest possible 

 support to the theory of the centrosome as an active stimulat- 



