CROSSING TWO HEMIPTEROUS SPECIES. 221 



to establish the claim that the intromittent organ can be classed 

 with the primary and not the secondary sexual characters. 

 This apparently ought not to be difficult, but a difficulty does 

 arise owing to the fact that recent authors who have discussed 

 secondary sexual characters have avoided defining them and 

 have neglected to state wherein they are to be distinguished from 

 the primary sexual characters. 



According to Darwin '59 Hunter defines secondary sexual 

 characters as follows: 



'The term, secondary sexual characters, used by Hunter, 

 applies to characters which are attached to one sex; but are 

 not directly connected with the act of reproduction." 



Darwin '86 adopts Hunter's classification of primary and 

 secondary sexual characters; but shows that even such an ap- 

 parently clear cut definition encounters difficulties. He says: 1 



"With animals which have their sexes separated, the males 

 necessarily differ from the females in their organs of reproduction; 

 and these afford the primary sexual characters. But the sexes often 

 differ in what Hunter has called secondary sexual characters, 

 which are not directly connected with the act of reproduction; for 

 instance, in the male possessing certain organs of sense or loco- 

 motion, of which the female is quite destitute, or in having them 

 more highly-developed, in order that he may readily find or 

 reach her; or again, in the male having special organs of pre- 

 hension so as to hold her securely. These latter organs of 

 infinitely diversified kinds graduate into, and in some cases can 

 hardly be distinguished from, those which are commonly ranked 

 as primary, such as the complex appendages at the apex of the 

 abdomen in male insects. Unless indeed we confine the term 

 'primary' to the reproductive glands, it is scarcely possible to 

 decide, as far as the organs of prehension are concerned, which 

 ought to be called primary and which secondary" (p. 253). 



Morgan '13 also appears to accept Hunter's classification, for 

 in his rather full list of secondary sexual characters he includes 

 none that are "directly connected with the act of reproduction." 

 He opens his discussion of secondary sexual characters as follows: 



1 The italics are ours. 



