364 EDMUND B. WILSON 



Largus and Pyrrhocoris but one dark body is seen; and this, as 

 I earlier showed in the latter case, is the unpaired X-chromosome. 



These massive bodies strongly suggest those to which Overton 

 ('05, '09) has given the name of ' prochromosom.es' in the case of 

 plant cells. Since however they differ from the latter in some 

 important respects I will not here employ this term; and for a 

 similar reason will not designate them by Strasburger's term 

 'gamosomes' ('05), though they undoubtedly give rise to the chro- 

 mosomes that enter synapsis. 



Even a casual inspection of these nuclei is enough to show 

 that the number of chromatic masses is not far from the sper- 

 matogonial number of chromosomes, while here and there a 

 nucleus may be found in which this number may be exactly 

 counted. The enumeration is most readily made in the case of 

 Largus cinctus where the spermatogonial number is eleven. 

 In this species, which has eleven spermatogonial chromosomes 

 (photo. 33), nuclei may readily be found in which ten of the paler 

 chromatic masses may be definitely counted. In L. succinctus 

 their number is often seen to be about twelve (the spermatogonial 

 number being thirteen). In like manner, the number of the pale 

 masses in Lygaeus is sometimes seen undoubtedly to be twelve, 

 in Oncopeltus about fourteen, the spermatogonial numbers being 

 respectively fourteen and sixteen, though in neither of these 

 species can the number be exactly determined in many cases. I 

 do not hesitate however to draw the conclusion definitely that in 

 these animals the full diploid number of separate chromatic masses 

 is present in a stage that shortly follows the last spermatogonial divi- 

 sion and precedes the formation of the leptotene-threads. In the 

 dragon-fly, Anax junius, there is a closely corresponding stage, 

 but in this case all of the chromatic masses stain nearly alike, and 

 the X-chromosome can often not be certainly distinguished until 

 a little later. 



The stage described above evidently corresponds to one in the 

 Orthoptera (Davis's 'Stage b' in Dissosteira, Chortophaga and 

 other grasshoppers) and is clearly shown in some of McClung's 

 slides. In all these forms, however, the chromatic masses stain 

 more deeply than in the Hemiptera, are of elongate form, and are 



