90 EDMUND B. WILSON 



latter being usually in close contact and in later anaphases some- 

 times hardly separable (50), though now and then all three compo- 

 nents are for a time strung separately along the spindle in the 

 early anaphases, so that no doubt of their distinctness can exist 

 (5 /) . Comparison of the diploid groups of the two sexes shows 

 that those of the male contain but three of these small chromo- 

 somes and those of the female four, the total respective num- 

 bers being 27 and 28 (instead of 16 in both sexes, as in the A 

 form). 



These facts make it perfectly clear that one of the small chromo- 

 somes in the male passes to the male-producing pole, and therefore 

 corresponds to the Y-chromosome; while the other two, taken to- 

 gether, represent the large idiochromosome, or X-chromosome, of 

 the A form precisely as in the reduvioids the single X-chromosome 

 of Diplocodus is represented by a double element in Fitchia, 

 Rocconota or Conorhinus (Payne). Had we no other evidence 

 on this point we might assume simply that the original X-chro- 

 mosome has divided into two equivalent X-chromosomes. But 

 there are other facts that give reason for the conclusion that the 

 breaking up of a single X-chromosome into separate components 

 means something more than this. In the B form, as in Fitchia or 

 Rocconota (fig. 5 I), the X-element consists of two equal compo- 

 nents, but in Conorhinus the two components are always of un- 

 equal size (5 ra). In Prionidus and in Sinea there are three equal 

 components (5 n, o), in Gelastocoris four equal ones (5 p, and 

 in Acholla multispinosa five, of which two are relatively large 

 and equal and three very small (5 r, s). In every case these com- 

 ponents, though quite separate in the diploid groups (and usually 

 also in the first spermatocyte-division) act as a unit in the second 

 division, though not fused, and pass together to the female-produc- 

 ing pole (Payne, '09, '10). 



In the foregoing examples the X-element is accompanied by a 

 synaptic mate or Y-chromosome. The following are examples of 

 a similar breaking up of the X-element into separate components 

 when such a synaptic mate is missing. In Phylloxera (Morgan) 

 the X-element consists of two unequal components, sometimes 

 separate, sometimes fused together. In Syromastes (Gross, 



