316 THOS. H. MONTGOMERY, 



outlined, and at the monaster stage (Figs. 175, 176, 179—182, Plate 22) 

 can be in many cases be no longer seen. There is no evidence that 

 any pole or other spindle fibres are formed from its substance ; and 

 there is good evidence against such a view in the fact that the centro- 

 somes do not show radiations until they have migrated out of the 

 idiozome cup (Figs. 128, 129—134, 138, 160—165, Plate 21; Fig. 134 

 shows the beginnings of the radiations). It would appear to dissolve 

 gradually in the cytolymph. Often portions of the idiozome mass may 

 be seen still at the distal pole of the cell as late as the monaster 

 stage (Fig. 179) ; and in one case a persistence of a portion of it was 

 noticed as late as the metakinesis of the second maturation division 

 (Fig. 207, Plate 22). 



It is at the commencement of the prophase that the centrosomes 

 make their first appearance as a pair of minute corpuscles, in the 

 centre of the cavity of the idiozome cup (Fig. 128, Plate 21). At 

 this stage they stain much more faintly than later: so that it is 

 quite possible that in the preceding rest stage they stained still more 

 faintly, and for this reason may then have escaped detection. The 

 pair of centrosomes increase in size, and take on the characteristic 

 deep ^stain with iron haematoxyline (Fig. 129). Next each one of 

 the pair elongates and constricts (Fig. 130) preparatory to a division 

 into two, which is accomplished while the centrosomes still lie within 

 the idiozome cup (Figs. 131, 132, 138). Then the two pairs of centro- 

 somes migrate to that surface of the cup nearest the nucleus (Figs. 131, 

 133, 134); this stage of their migration was found most abundantly 

 in my preparations. I could not determine whether the centrosomes 

 reach the surface of the cup-shaped idiozome mass by migrating 

 through its opening, or by moving directly through its wall; the dif- 

 ficulty in the observation lies in the fact of the irregularity in position 

 of the axis of the cup, and the irregularity in its form. But in some 

 cases at least the centrosomes migrate through its opening, as in 

 those cases where the two pairs of centrosomes can be clearly seen 

 just opposite the outer opening of the cup (Fig, 134). An axis joining 

 the two centrosomes of a pair is now more or less parallel to the 

 surface of the idiozome cup; and the two pairs of centrosomes are 

 more separated than they were before. Then the two pairs of centro- 

 somes leave the surface of the cup and pass towards the nucleus 

 (Figs. 160 — 162). It is after leaving the surface of the idiozome cup 

 that cytoplasuiic radiations, pole fibres, first become apparent around 

 each pair of centrosomes (Figs. 134, 160—165), the distal terminations 



