306 DIMORPHISM IN FEMALE OF ISCHXURA HETEROSTICTA. 



One of two things, then, seems to have happened. Either, 

 firstly, Form A is the original specific female, in which case Form 

 B may have been evolved as a protective form, mimicking the 

 males because of the latter's immunity from destruction; or, 

 secondly, Form B, resembling the male so remarkably, was the 

 original specific female, in which case Form A may have developed 

 its sombre colouring as a protective garb for the preservation of 

 the species, the typical female being particularly liable to destruc- 

 tion from its brilliant colouring. We must then suppose that 

 the male, being less palatable and attractive, had no need of a 

 protective guise, and therefore remained constant in form and 

 colouring. If the second supposition be correct, we should expect 

 the protected form of the female to become more abundant and 

 more fertile than the unprotected form. This is at present the 

 case, Form A being by far the more abundant, and the stouter 

 and more developed abdomen indicating greater fecundity. 



As regards the distribution of the two forms, Form A occurs 

 wherever the male insect has been taken. Form B was found to 

 be fairly common at Cook's River on my first visit in February 

 last, but a second visit only yielded one specimen, while Form A 

 was still very abundant. Form B also occurs sparingly at 

 Mittagong, and will no doubt be found in many other localities. 

 It is most difficult to distinguish it from the male except by 

 careful examination, and hence the fact that it has been so long 

 entirely overlooked. 



