64 Dr. Veiloi'cn on the Comparative Influence of 



between 4 and 7 in the evening, which has been proved by ex- 

 periments of my own. 



To determine this more accurately it is necessary to make ob- 

 servations on a great number of individuals. During several 

 years I have made them upon Sphinx Ligustri, and I have obtained 

 very curious results, showing evidently an influence determined 

 only by the time of the year, without any influence of the tem- 

 perature. The perfect moths do not always come out in the fol- 

 lowing year, but some remain in the pupa to the second year. 

 The time of coming out is ordinarily the last half of June ; those 

 which have not come out at that time remain to the following 

 year. In July and August a sufficiently high temperature is 

 developed, but it is without influence, if their determined time has 

 passed, and they remain to the following year, when they come 

 out precisely at their determined time in June, simultaneously 

 with those which have undergone their transformation to the 

 pupa in the preceding September. 



During the years of 1844 — 1852, out of 236 pupae 182 came 

 out in the year subsequent to their pupation, 40 in the second 

 year, and 14 died; thus 18 per cent, of the whole number of 

 pupae remain to the second year. 



The mean time of coming out has been found to be the 21st 

 of June, and the limits of appearance the 4th of June and the 19th 

 of July. The year 1851 was especially backward, and the latest 

 limit of the 19th of July occurred in that year, whilst the first 

 specimen came out in that year on the 25th of June. The year 

 1848, on the contrary, was the most forward, and the moths 

 appeared from June 4th to June 26th. As stated before, the two- 

 year brood came out in every year exactly at the same time as the 

 one-year brood. [^See Table opposite.^ 



In the one-year brood the males have always been about a week 

 in advance ; in the two-year brood no marked difference could be 

 observed in this respect. Although it seems to be the rule, that 

 in most insects the males precede the females, there are also 

 instances where the reverse is the case. Out of twenty pupae of 

 Psyche nitidella which I reared, ten females came out between the 

 1 4th and 20th of June ; the following week not one came out; 

 and after that time only males were developed. During the past 

 year I made observations upon a certain number of pupse of 

 Papilio Machaon with the like result. 



The general relation between the number of males and females 

 of Sphinx Ligustri which I reared was, as 53-85 per cent, ^ to 

 46"15 $ ; but between the one and two-year brood the prepon- 



