58 EDMUND B. WILSON 



3. An odd or accessory chromosome is present, and also a 

 third w-chromosome. 



A study of the maturation process decisively establishes the 

 third of these possibilities as the fact. 



b. The first spermatocyte-division 



Both testes contain immense numbers of both spermatocyte- 

 divisions in all stages, and many of the cysts show the facts with 

 great beauty. The first division itself at once indicates the true 

 interpretation of the spermatogonial groups; and this is consis- 

 ently borne out by the stages which precede and follow. 



In polar views (fig. 2, d-g] the first division metaphase is iden- 

 tical in appearance with that of Anasa, Chelinidea, Narnia, and 

 other coreids that have 21 spermatogonial chromosomes (including 

 Montgomery's individuals of M. terminalis). Eleven chromo- 

 somes appear, including one very small central one surrounded 

 by a ring of nine much larger ones, while the eleventh usually 

 occupies a position outside the ring, as in figs. 2d, 2f, (figs. 2e, 2g 

 are given to show exceptions to this). From these views alone 

 we should infer that the spermatogonial number is 21, that the 

 small central chromosome is the m-bivalent, and that the eccentric 

 one is the accessory. This will appear upon comparison with 

 figs. 2, h, i, which show two corresponding views of Montgomery's 

 material of M. terminalis. Side views at once reveal the fact, 

 however, that the central body in No. 64 is not a bivalent but a 

 triad element, consisting of three small chromosomes united end 

 to end (figs. 2b, 3a, &,) and it is perfectly evident that these are 

 identical with the three very small ones of the spermatogonial 

 groups. Hundreds of these figures have been observed, iri almost 

 all of which the three components have the linear arrangement 

 just described; but now and then a different grouping occurs, as 

 may be seen in both side (fig. 3c) and polar views (fig. 2g). 



In the ensuing division the ten larger chromosomes divide 

 equally, showing as they draw apart the curious forms represented 

 in fig. 4, which are closely similar to those described in Anasa 

 by Paulmier ('99). As the figures show, the chromosomes in 



