194 KANSAS UNIVERSITY SCIENCE BULLETIN. 



the mantle fibers running to the centrosomes. The changes 

 now ensuing are easily decipherable, because the chromosomes- 

 do not all undergo division at the same time. Since the main 

 differences at present existing between insect spermatologists 

 relate to the sequence of the divisions in the spermatocyte 

 mitoses, I shall again describe the process, although it is iden- 

 tical with that already given for Hippiscus. 



The necessity for a thorough understanding of the chromo- 

 some construction here becomes evident. Knowing how the 

 chromatids were associated in the chromosomes, one can follow 

 understandingly their movements during metakinesis. 



It is first to be noted that the chromosomes lie with their 

 longer axis in the equatorial plate. This, as we have seen, is 

 the plane along which the longitudinal cleft occurred, so that 

 a separation in this way means the longitudinal division of the 

 chromosomes in the first spermatocyte. This is, in reality, 

 what occurs. The contracting mantle fibers attached to the 

 middle of the segments drag the adhering chromatids apart 

 without at any time exposing a separating space. It is in this 

 way that in the beginning the longer axes are at right angles 

 to the spindle axis and at the end parallel with it, while dur- 

 ing intermediate periods crosses with arms of varying length 

 exist (figs. 13, 34) . 



The previously disguised lines of separation become at once 

 visible in the daughter chromosomes, for, instead of remaining; 

 closely apposed, as formerly, the chromatids spring apart at 

 the free ends and the chromosomes pass through the anaphase 

 as V-shaped bodies instead of as simple rods. The space thus 

 disclosed represents that which separates what would be the 

 ancestral spermatogonial chromosomes, assuming that the re- 

 duced number occurs by the end-to-end union of chromosomes 

 of the secondary spermatogonia. As already stated, the acces- 

 sory chromosome does not divide at this time. 



At the end of the anaphase we find the ordinary chromo- 

 somes massed at the poles of the cell, and, in addition, at one 

 the undivided accessory chromosome. The second spermato- 

 cytes are therefore of two kinds, one possessing the accessory 

 chromosome and the other not. One additional feature of in- 

 terest that becomes apparent during the migration of the daugh- 

 ter chromosomes to the poles is the retarded division of one 



