J. W. H. Harrison 41 



As will be seen below, to the first and second questions I obtained 

 a decidedly negative answer: in the case of the third, although not pre- 

 cisely the same as those with which comparison was desired, my results 

 showed a considerable approach thereto in a broad fashion. The answers 

 to the fourth will manifest themselves as the facts of the experiments 

 are gradually unfolded. 



11. Technique Employed. 



For several reasons, some personal and some arising from the war, 

 after a short while it was deemed best that I should restrict myself to 

 the use of ethyl alcohol throughout the work. At first sight, the diffi- 

 culties attending the administration of this compound to lepidpptera 

 seemed insuperable, and indeed are so if one wishes to employ the agent 

 in the liquid form ; these obstacles, however, quickly vanish if one con- 

 siders the ease with which insects are affected at any stage of their 

 life-histories by the vapours of chloroform, ether, hydrocyanic acid, 

 sulphur dioxide and the like. The only trouble remaining is to devise 

 some means of regulating the dose and of ensuring that its incidence is 

 long enough. Here the advantages of utilising a Geometrid moth 

 appertaining to such a hardy genus as Selenia are at once realised ; a 

 considerable number of their larvae can be reared in airtight cages with- 

 out the slightest ill-effects manifesting themselves. If once the use of 

 airtight cages is granted methods of generating constant and steady 

 supplies of alcohol vapour so that ova, larvae, and pupae are always 

 under its action are very simply designed. After a few preliminary 

 experiments to determine the optimum quantity to be employed, one 

 readily finds that by saturating a small sponge periodically with definite 

 quantities of alcohol the atmosphere within the cage is kept uniformly 

 charged with the fumes. Thus the creatures are never at any period 

 of their growth and development free from its possible influence either 

 on their germ or on their somatic cells. Only one precaution is necessary, 

 and that is to suspend the sponge so that the larvae can never come into 

 contact with the liquid used, which, in my case, was the ordinary 90% 

 non-methylated ethyl alcohol of the chemist. 



To secure the larvae experimented with, a healthy male and female 

 Selenia bilunaria were taken from a brood once inbred and paired ; the 

 female in due course laid over a hundred fertile ova. In order to avoid 

 overcrowding as far as possible, ninety of these were divided into two 

 random batches of forty-five, one to be submitted to the alcohol regimen. 



