BY R. J. TILLYARD. 



347 



moreover in which the proportion of two to one in favour 

 of the male can easily be shown to prevail in the case of 

 the perfect insect. I have taken this insect in man}^ localities 

 around Sydney, and wherever it occurs I have found the males 

 far more numerous than the females. The result obtained then 

 by breeding out a number of the nymphs should carry great 

 weight. During last season I kept in my aquarium about a 

 hundred nymphs of this species. These nymphs were taken from 

 waterholes and small creeks without any selection of the darkest 

 or largest forms; in fact every specimen brought out of the 

 water by the net was put into the aquarium. One only, a fine 

 and healthy specimen of a very dark form, was separated from 

 the rest and put into a small jar for observation. During August 

 and September of last year many of these nymphs emerged from 

 the aquarium. The period of observation was just one month, 

 from August 8th to September 7th, none emerging after the 

 latter date. The following is a careful record of the sex and 

 date of appearance of the specimens : — 



One of these, the male that emerged on Aug. 1 3th, was the 

 one that had been specially selected and separated for observa- 

 tion. Since he had the advantage over the others in an abund- 

 ance of food, which the others certainly had not, and since he 



