GERM CELLS IN ASCARIS INCURVA 81 



plates united by taut interzonal fibers, but the X-group except- 

 ing its long member lies midway of the spindle and parallel to 

 the autosome plates (figs. 38 and 39 and text fig. B). From 

 either pole there proceeds to this group a central core of spindle 

 fibers which with the interfibrillar substance forms a most strik- 

 ing picture that can not adequately be figured. The spindle 

 fibers are attached to either side of each of these chromosomes. 

 Meanwhile one end of the long X-component has retained its 

 place in one of the receding autosome rings (its mate the Y 

 lying in the opposite ring) wl.ile the other end remains united 

 to the remainder of the X-group, thus forming a connection 

 between these latter chromosomes and the anaphase plate with 

 which they will ultimately unite. During this process the spindle 

 appears to shorten — the average of measurements of 70 meta- 

 phase spindles from centrosome to centrosome is 12.3 microns; 

 that of the early anaphase spindles when the separation of auto- 

 somes was not greater than 5 microns, is 11 microns. Later 

 the spindle elongates, rapidly to about 18 microns (see note 4, 

 page 82) . 



b. The second phase. After the stage of figure 38 and 39 

 a marked change appears, the cleavage furrow appears, the spindle 

 fibers become bent, broken and rapidly disappear (figs. 40, 41 

 and text fig. C) . The X-group is relaxed from its position parallel 

 to the autosome plates and swings as though pulled from the 

 outer end of the long component by the receding autosome plate 

 until it assumes a position parallel to the spindle axes (figs. 

 41, 42). Figure 40 shows the spindle fibers persisting more 

 clearly than usual and it will be observed that those attached 

 to the X-group are bent and also that a vesicle appears to form 

 about the X-group usually being more noticeable on the side 

 towards the pole from which it is receding. Figiu'e 43 shows 

 the network of linin threads uniting the X-chromosomes. The 

 division is then completed and the chromosomes become re- 

 arranged in the equatorial plate of the secondary spermatocyte 

 without entering the resting condition. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, XO. 1 



