74 W. W. SWINGLE. 



the metaphase plate along with the other chromosomes. The 

 X-body is readily detected at this stage by reason of its marked 

 dumb-bell appearance. 



Shortly before the chromosomes split, the dumb-bell-shaped 

 X-body migrates to one or other pole of the cell, far in advance 

 of the other chromosomes, and comes to lie at the apex of the 

 spindle close to the centrosome (Figs. 14-19). Lateral views of 

 such spindles, with the chromosomes at the metaphase, are 

 difficult to count; the larger chromosomes obscure the smaller 

 in many instances. Usually, however, twelve obviously bivalent 

 chromosomes can be counted at this stage, in the equatorial 

 region of the cell, just previous to splitting of the chromosomes, 

 and one large, dumb-bell-shaped .X-body, the accessory, at one 

 or the other pole. 



The resulting division separates the twelve bivalents into 

 halves, each half migrating toward its respective pole. As a 

 result of this division, an unequal distribution of chromatin to 

 the secondary spermatocytes occurs; one cell receiving twelve 

 chromosomes plus the dumb-bell X, the other cell receiving 

 twelve ordinary chromosomes. 



A late anaphase of the first spermatocyte division, showing 

 the X-body at one pole of the anaphase, the other pole without 

 the accessory, is shown in Fig. 20. 



The dumb-bell X-body is very conspicuous in many cells in 

 late anaphase stages. It retains the dumb-bell shape, whereas 

 the remainder of the chromosomes are comparatively small, 

 single bodies. In late telophase stages of the first maturation 

 division, all individuality of the chromosomes is lost; the chro- 

 mosomes clumping together to form a somewhat irregular cres- 

 cent. In many such stages the accessory chromosome is easily 

 located by the fact that it is so large that half of it projects from 

 the chromatin mass. It may lie horizontal to the long axis of 

 the cell, resting on the other chromosomes, or at times partly 

 imbedded within their mass. 



Three first spermatocyte divisions were observed in which the 

 X-body appeared as a single and not a dumb-bell-shaped chromo- 

 some. Figs. 21-23 show the single nature of the X chromosome. 

 In these cells, the X is just half the size it appears in other cells. 



