m'clung: spermatogenesis of xiphidium fasciatum. 259 



the chromatids of this element, usually more prominently at 

 the ends, while at the center they remain in contact. The re- 

 sult is to produce a structure that looks like two U's with their 

 rounded ends in contact, A careful study shows that this is 

 merely an apparent condition, for other cells have the accessory 

 chromosome with the chromatids parallel (fig. 12). The ordi- 

 nary chromosomes become very loose and granular, but their 

 outlines may still be seen indistinctly, 



second spermatocytes. 



The prophase of the second spermatocyte is very brief, ap- 

 parently, and soon the chromosomes have taken on their homo- 

 geneous condition, and have arranged themselves in the ec[ua- 

 torial plate. Only rarely, however, do they show the sharp 

 outlines found in chromosomes of the preceding cell genera- 

 tion, but more frequently tend to coalesce somewhat. A polar 

 view of the metaphase shows a compact plate of chromosomes 

 with the large ones on the periphery. In those cells possessing 

 the accessory chromosome there is added this element to the 

 peripheral series. In form the accessory chromosome is V- 

 or U-shaped, with the apex directed toward the center of the 

 spindle (figs, 13, 14, 15), When viewed from the side the V- 

 or U-shaped element is discovered to be double. The ordinary 

 chromosomes are again dumb-bell-shaped (fig, 16). 



An inspection of an early anaphase of the second sperma- 

 tocyte shows that the mantle fibers attach to the center of the 

 chromatid in the accessory chromosome, and division com- 

 mences therefore at this point. In mid-anaphase the accessory 

 chromosome has accordingly the form of two V's with their 

 apices directed away from each other and toward the poles of 

 the spindle. Still later the separated V's are found with the 

 other chromosomes at the poles of the spindle. Even in the 

 telophase they remain in this form and position after the other 

 chromosomes have fused together in a mass. The plane of 

 separation is unquestionably the longitudinal cleft, visible most 

 prominently in the telophase of the first spermatocyte. In 

 those second spermatocytes from which the accessory chromo- 

 some is absent, the chromatin elements divide almost syn- 

 chronously and pass to the pole of the spindle in a mass. The 

 presence of the accessory chromosome, which divides later than 

 the other chromosomes, tends to retard division on its side of 



