148 H. H. COODRICH. 



of the plate divide equally, thus forming two anaphase plates of 

 thirteen chromosomes, typically arranged in a ring except that 

 at a point of one daughter plate a gap is observed, opposite 

 which in the other plate is a fourteenth chromosome (Figs. 4 and 

 6). There remain eight chromosomes lagging in the center of 

 the spindle and arranged in a characteristic plate consisting of 

 six chromosomes of the average size, the microsome and a larger 

 long chromosome arranged in an approximately oval or circular 

 plate with the long chromosome projecting from the periphery 

 (Figs. 5 and 8). As the daughter plates separate, this peculiar 

 group tips, apparently as a unit, so that the long chromosome 

 approaches the gap in the ring of thirteen autosomes. Event- 

 ually this whole group passes to the center of the ring and 

 thus the two daughter-cells (second spermatocytes) receive 

 respectively 14 and 21 chromosomes. Size relations and position 

 facilitate the identification of homologous daughter chromosomes 

 of the anaphase plates when these are observed superimposed 

 within a single section (Figs. 4 and 6). Thus the thirteen auto- 

 somes of either daughter ring may be readily identified, and, by 

 elimination, the fourteenth of one ring unmated in the other. 

 This fourteenth chromosome must therefore be considered as a 

 Y-chromosome mated by that, member of the X-group, the long 

 chromosome, which is first inserted into the gap of the one ring, 

 corresponding to the space occupied by the fourteenth chromo- 

 some of the other. Side views of metaphase figures of this divi- 

 sion (Fig. 3) show the Y-chromosome lying opposite one end of 

 its longer mate to which it may be united. Fig. 3 is an optical 

 section of such a group showing the Y, its long mate, six other 

 elements of the X-group massed and undivided, surrounded by 

 certain of the dividing autosomes. A cleft in the X-chromosomes 

 indicating the line of division in the ensuing second spermatocyte 

 division may often be observed in the anaphase stage of the first 

 division (Fig. 8). The long chromosome splits lengthwise and 

 usually the chromatin appears concentrated at either end of each 

 half giving a quadrivalent appearance and suggesting a tendency 

 to separate in two parts, one to remain the mate of the Y and 

 the other to increase the number of those unmated. 



From the foregoing it will be clear that the secondary spermato- 



