GERM CELLS IN PEDICELLINA AMERICANA 15 



The spindles elongate, and the bars arc drawn out across the 

 equator, a thin strand connecting the dyads. This soon disap- 

 pears, leaving the halves as thicker, almost spherical bodies 

 drawn out to an end in the direction of the division plane 

 (Figs. 41-42). While this is the usual form, in some instances, 

 other structures are presented in which the true double nature 

 of the bodies is more distinctly brought out. Thus, as in Fig. 

 43, one of the dyads is a short U. This is evidently a case 

 where the transverse division occurred before the ring had elon- 

 gated sufficiently into a bar. The dyads move to the poles, 

 and the first division is at an end (Figs. 44-46). Here the 

 chromosomes are densely crowded together, and in the late 

 telophase (Fig. 46) the study of the individual chromosomes is 

 quite impossible. 



Judging from the rarity of its occurrence in the testis, this 

 stage is one of short duration. The second maturation figures 

 (Figs. 47-54) are about one half the size of those of the pre- 

 ceding division and are at this early period of a spindle shape. 

 The chromosomes appear as the reduced number of rods or bars, 

 showing a distinct constriction in the middle, and have arisen 

 by the further concentration of the dyads, very probably dur- 

 ing the last telophase. In a cross section of the spindle in the 

 metaphase (Fig. 48) the eleven rods are even more distinctly 

 seen. These lie in the spindles that the constrictions are in the 

 plane of division. The chromosomes are therefore so directed 

 that this division is longitudinal, separating the sister monads 

 which had arisen by the splitting of the arms of the primary 

 V's in the early periods of spermatocytic growth. In the early 

 anaphase, the two halves of the rods begin to move apart, leav- 

 ing a thin strand of chromatic substance between (Fig. 49). At 

 the same time, the monads still further condense, and with the 

 complete division, in the middle anaphase, give the appearance 

 of small spheres (Figs. 50— 5 2), the chromosomes dividing quite 

 synchronously. In the telophase (Fig. 53) the spherules have 

 arrived at the poles, but do not as yet show any sign of fusing 

 into one mass. This does not occur until a somewhat later 

 period (Fig. 54) when the cytoplasm shows the characteristic 

 constriction separating the two resulting spermatids. 



