EACES OF MOSQUITOES 293 



which is at variance with Roubaud's conclusion that a gradual 

 decrease in the number of females produced in successive genera- 

 tions followed prolonged continuous autogeny. The feeding of 

 the females with fruit juice is apparently without influence on 

 egg-production, but after a blood-meal the number of eggs in a 

 raft is about twice as many. The males pair with resting females, 

 and it is evident that mating can occur in very small vessels or 

 restricted areas. The females are voracious blood-suckers of 

 both birds and man. Tate and Vincent regard the term autogeny 

 as being unfortunate, owing to its being a variable character, 

 since on an average only 60 per cent, of the females lay autogenous 

 eggs and under unfavourable conditions very few may do so. 

 They consider that eurygamy and stenogamy are more constant 

 characters for differentiating between the two races. Roubaud 

 (1935) has described differences in the micro-structure of the egg- 

 floats of the two races, and Marshall and Staley (1935) found 

 differences in the chsetotaxy of the larvae. 



Reciprocal cross-mating between individuals of the sexes of the 

 two races was easily obtained. The experiments show that 

 autogeny and stenogamy are genetical characters transmitted to 

 the progeny. Stenogamy always appears in the F^ generation, 

 but autogeny may not appear until the Fg generation or later. 

 Much further genetical work is necessary, however, before the 

 inheritance of the racial characters can be discerned with 

 confidence. 



The question naturally arises as to the evolutionary significance 

 of biological races. Do they, in fact, afford evidence of evolu- 

 tionary divergence which, if carried far enough, will ultimately 

 lead to the production of new species ? A number of workers have 

 answered this question in the affirmative. If, at any rate, some 

 of the races are species in the making, and where their characters 

 are germinally fixed there seems good evidence for this view, we 

 have to conclude there is some degree of isolation of a physiological 

 or behaviouristic kind which ensures their continuance. None of 

 the evidence so far presented provides sufficient data to carry 

 full conviction in this matter. It does, however, suggest a 

 profitable field for further enquiry, and for a discussion of the 



