144 Mr. F. Merrifield's systematic, temperature 



while large ones found late in the season are almost 

 sure to be females. 



In some autumnaria (Table VII.) that were cooled 

 for a period of 28 days there was a similar difference, 

 only slightly greater, averaging 2^ to 3 days in favour 

 of the female. 



In some alniaria (Table XII.) the difference was 

 greater still, amounting (in some that had been cooled 

 for 28 days) to an average of 4 daj'^s in favour of the 

 female. 



In illustraria, comparing 25 iced males with 15 iced 

 females, I find that the former averaged 12'2 days from 

 the time of being taken out of the ice, the latter 

 10-6 days. 



(2) Sloiv development of the pupa during the icing 

 period. — My experiments do not enable me to measure 

 this accurately, as the temperature to which the pupje 

 were exposed, after being taken out of the ice, varied 

 with the varying temperature of the year. As far as I 

 can guess, I should say that 120 days at 33° represent 

 as regards progress in time for development certainly 

 not more than 3 days at 65°. 



(3) Obscurity of the causes on which the vigour of a 

 brood may depend. — I add some observations on the 

 deterioration in some cases of the heredity broods of 

 illustraria, because it is of general importance to all 

 who are bringing up larvae for scientific and other pur- 

 poses to get, if possible, at the causes of this deterioration 

 with a view to its prevention. All who have bred on a 

 considerable scale are familiar with it as a frequent 

 result with many species, but by no means with all, 

 especially when care is taken, as it has been with my 

 illustraria, to bring them up under the most favourable 

 conditions. The second generation of those bred in 

 captivity, i. e., the larvge fed in the autumn of 1887, 

 produced remarkably large and healthy moths, the 

 largest I have ever seen. There was some falling off in 

 health and size in the next emergence (July, 1888), and 

 a very great falling off in both respects in the following 

 autumn-fed brood. Since then the health and size 

 have continued with those bred by me to be about the 

 same, that is, poor. But the circumstance I wish par- 

 ticularly to call attention to is that the deterioration in 

 some cases, which I should be glad to account for, has 



