DAVIS : SPEmiATOGENESIS. 101 



metaphase of the first di\-ision the monosome may he either in the plane 

 of the equatorial plate midway between the spindle poles or nearer 

 one pole than the other (Plate 4, Fig. 63). Even when it lies in the 

 eciuatorial plane, the monosome can be easily distinguished by its 

 rough contour, and also by the fact that it usually lies with its axis 

 at an angle to the axis of the spindle. In all cases the monosome is 

 attached to spindle fibers from only one pole. The monosome does 

 not divide during the first maturation division, but passes bodily to 

 one of the poles (Fig. 65). In Figures Ma-Mc (p. 96) which are all 

 drawn from sections of the same cell, this is conclusively shown. 

 Here there can be no doubt that all the chromosomes except one have 

 divided into two equal parts, which are mo\'ing toward opposite poles 

 of the spindle. The other chromosome, the monosome, has no corre- 

 sponding mate moving toward the opposite pole. As the monosome 

 passes toward the pole the arms of the U separate somewhat, so that 

 it has practically the same shape as the autosoiBcs. In the succeeding 

 telophase the monosome cannot be distinguished, but in the "semi- 

 resting" stage of the secondary spermatocyte it can again be recog- 

 nized. During this stage the monosome retains its compact structure 

 in striking contrast to the autosomes. During the second maturation 

 division the monosome is not distinguishable, since the autosomes also 

 have at this time somewhat rough contours. Figure R (p. 100) is a 

 polar view of the equatorial plate of a secondary spermatocyte which 

 lacks the monosome, there being only eleven chromosomes present. 

 Figure Q is a similar ^■iew of a cell with twelve chromosomes, one of 

 which is evidently the monosome. During the second division the 

 monosome divides along with the autosomes. This is conclusively 

 shown in Plate 5, Figures 78 and 79, which are drawn from two sec- 

 tions of the same cell. In this case there can be no doubt that there 

 are twelve daughter chromosomes passing to each pole of the spindle. 

 The question at once arises, are we to consider the division of the 

 monosome during the second maturation division longitudinal or 

 transverse. Otte (:06) concludes that in Locusta, where the mono- 

 some has a somewhat similar history, the di^'ision is transverse. At 

 first I was inclined to interpret the division in Dissosteira in the same 

 way, but on further consideration believe such a conclusion to be un- 

 warranted. The peculiar manner in which the monosome becomes 

 converted into a loop during the latter part of the growth period can 

 be easily interpreted as due to a longitudinal splitting. This interpre- 

 tation is supported by the fact that, whereas the autosomes become 

 converted into a single chromatin thread, the monosome becomes 



