20 Studies in the Hybrid Bistoiiinae. IV 



This simply means that' accompanying the racial difference there 

 must be a physiological divergence, and this was confirmed most strongly 

 by the significant difference in the products of the back cross between 

 hybrid pilzii male and hirtaria female when the hirtaria blood in the 

 pilzii was of Scotch origin, and when it was from another source. 



With this physiological difference, or rather as a special item in it, 

 the observed facts state unequivocally that a distinct alteration of the 

 powers of the sex genes has occurred, so that, in crossing pomonaria 

 males with Scotch hirtaria females, we are not reproducing the circum- 

 stances attending similar crosses in which English hirtaria are concerned ; 

 we seem rather to be imitating the conditions of the crosses between 

 hirtaria ^ and zonaria $ which, as we saw, yielded wholly male families. 



If this explanation of anomalous broods be valid, i.e. that it depends 

 on a racial variation of the powers of the sex determiners, then it is 

 reasonable to suppose that there must exist other local races of insects 

 displaying similar discrepancies in sex potencies, and such is the case as 

 Brake, Poppelbaum, Goldschmidt, and Muschamp found in their mongrels 

 between Lymantria dispar and its Japanese local race var. japonica. 

 What seems of special import in this instance was the obtaining of 

 intersexes. 



On the Status of the P. pomonaria Male x L. hybrid pilzii Female Brood. 



Before proceeding to the consideration of the intersexes obtained as 

 the progeny in this cross, it will be well to glance for a moment at the 

 structure of the genitalia of both sexes in this group. Fortunately, 

 this is simple in both cases and need not detain us long. 



Male structures. Text-fig. 1, male genitalia of L. ursaria. 



In this figure, diagrammatic almost in its simplicity, will be noticed 

 a terminal pointed portion ; this is termed the Uncus and it represents 

 the tergite of the 10th abdominal segment. Attached to its base 

 appears a chitinous collar provided with a chin-like projection impressed 

 with scale -like hollows; to this organ the name Gnath or Gnathos is 

 applied. Just anterior to the uncus is the Cingulum or Tegumen Ring 

 replacing the 9th segment ; the basal or sternal portion of this structure 

 is thrown forward into the abdomen to form a kind of hollow or pouch 

 known as the Saccus. Articulated more or kss with this tegumen are 

 the Penis and its members. The penis, i.e. the whole organ, Aedoeagus, 

 vesica, cornuti combined, may be seen lying to the left of the figure, 

 between the uncus and the left valve or clasp. Projecting from the 



