experimenU on some Lepidopter<i. 145 



given place to an opposite result. Some broods, which 

 with me had become a mere remnant, few in number 

 and small in size, produced eggs, which I sent to my 

 friend Miss Pridham, of Wimbledon, who has been 

 rendering valuable aid in these experiments, and these 

 have produced much larger, more numerous, and more 

 healthy moths, and that not in one case, but in several. 

 The only difference that I can see in the treatment is 

 that they have been sleeved on old cherry instead of 

 young birch, and have been in a rather warm situation. 

 But none could have been finer than those I reared on 

 young birch in a cool situation in 1887. After much 

 consideration I cannot see that either interbreeding, 

 kind of food, crowding, temperature, moisture, change 

 of locality, or any other circumstances I can think of, 

 account for the difference. The fact that the deteriora- 

 tion is not continuous is encouraging, and I shall be 

 very much dissatisfied if, with the kind suggestions of 

 members of this Society, the cause of it cannot be 

 ascertained, for the benefit of myself and others. I have 

 always thought that the causes of the wholesale deaths 

 one reads of in narratives of larval bringing up, for 

 example, in the late Mr. Buckler's work, require more 

 investigation than they have received. The only con- 

 jecture I can make as to this particular case — and it is 

 a conjecture only — is that possibly illustraria requires a 

 change of diet after a generation or two. There are 

 indications of a liking for such change in individuals ; 

 larvae beaten from oak showed with me a decided 

 preference for birch and willow, and some brought up 

 on birch took to rose in their last stage. 



Some General Conclusions. — I venture to submit 

 some of the principal conclusions of a general kind to 

 which the experiments recorded in this paper and in 

 previous ones seem at present to point. As to some 

 there will probably be little or no difference of opinion, 

 and as to others, no doubt further experiment is neces- 

 sary, and their apparent results require also to be con- 

 sidered by the light derived from a knowledge of the 

 habits and life-histories of many other species than 

 I have any experience of. The Tables in the Appendix 

 show in detail the facts as regards each individual in 

 many of the broods operated on by me, with the results 

 stated. They will enable others to judge how far my 



TRANS. ENT. SOC. LOND. 1890. — PART I. (APRIL) h 



