78 Edmund B, Wilson 



distinguished; but in some cases they may still be seen, as in Photo 

 12. As the nuclear vacuole forms the ordinary chromosomes 

 rapidly diminish in staining capacity, while the idiochromosome 

 bivalent retains its compact form and dark color, like a nucleolus, 

 and thus comes conspicuously into view, particularly after safranin. 

 Its double nature is at this time often more clearly apparent than 

 in the preceding stages. It disappears from view some time after 

 the reconstruction, at a much earlier period than in Pyrrochoris. 



Only exceptionally in my preparations do the chromosomes of 

 the second division show a quadripartite form as Gross figures 

 them. Their usual form is dumb-bell shaped or dyad-like; 

 though as the two halves separate they are often connected by 

 double fibers, as is the case with many other species of Hemiptera. 



PYRROCHORIS APTERUS L. 



As already stated, Pyrrochoris is of different type from Syro- 

 mastes and agrees precisely with other forms having an unpaired 

 idiochromosome, such as Anasa or Protenor. Aside from the 

 interest that this species possess as the one in which Henking first 

 discovered the idiochromosome, it is in other respects a peculiarly 

 interesting form for the study of the general spermatogenesis, 

 particularly in respect to the presynaptic and synaptic periods. 

 I shall here, however, confine myself mainly to the numerical 

 relations and the history of the idiochromosome. Henking him- 

 self somewhat doubtfully concluded that the spermatogonial 

 number was twenty-four: "Ich habe in drei Fallen die Zahl 24 

 erhalten, in einem Falle die Zahl 23. Da die Bilder iiberall die 

 gleichen sind, so habe ich das Zahlgeschaft nicht an einer grosseren 

 Zahl vorgenommen und glaube die theoretisch zu erwartende Zahl 

 24 als das Normal ansehen diirfen" (op. cit., p. 688, italics mine). 

 It is clear enough from this that Henking, too, was misled by a 

 false theoretic expectation; and a study of his figures (op. cit., 

 Figs. 6, a, b. c, 7) will show that they are very far from decisive. 

 In the case of the female, Henking speaks much more positively 

 ('92) and there is hardly a doubt that his count of twenty-four 

 chromosomes was correct, since he found this number "unverkenn- 



