THE ENTOMOLOGIST. 261 



On the 4th of this month (April) I placed them in a box on a 

 warm chimney-piece, and this morning (9th), to my great 

 astonishment, a small but perfect insect made its appearance, 

 having remained in its dark cell three years and a half, and 

 having in the meantime travelled from Cubley to Torquay, back 

 again to Cubley and thence to Dublin. 1 have called this an 

 extraordinary case, and, as regards this species, I should say 

 unexampled. The occasional prolongation as well as ac- 

 celeration of the pupal state (especially among the Bom- 

 byces) is of course a fact well known to all Lepidopterists, 

 and we find both to occur not unfrequently in the genus 

 Notodonta; but during many years breeding of most of 

 the species contained in it, I have never known the 

 prolongation to extend beyond the second year. What 

 can be the cause or causes of this retardation and accele- 

 ration ? The apparently obvious explanation would be, 

 cold in the former case, heat in the latter. But it is very 

 clear that this solution will not apply to the case cited above, 

 for these pupae displayed an obdurate and callous indif- 

 ference to two of the hottest summers {'66 and '68) we have 

 had for many years. A subject kindred to this, and present- 

 ing even greater difficulties in the way of explanation, is the 

 unexpected appearance (in certain seasons) of rare insects. 

 When asked the reason of this, most people will com- 

 placently and thoughtlessly answer, " Oh, it is owing to the 

 unusually hot season." I say thoughtlessly, for, assuming 

 this to be the case, which I neither admit nor deny, can they 

 further explain why it is so ? I have lately read in the 

 'Student and Intellectual Observer' (vol. ii. 1869, p. 180) 

 an interesting and intelligent paper on this subject by Mr. 

 E. C. Rye. In the opening part of it he speaks of the tem- 

 porary (/mppearance of certain water-loving insects, owing 

 to lack of moisture caused by unusual and protracted heat. 

 This is obvious enough. He then remarks that one effect of 

 unusual heat is acceleration of metamorphosis, and that a 

 conspicuous illustration of such acceleration is the increase 

 of broods, consequently increase of numbers of individuals 

 in any species. This seems, at first sight, fair enough ; but 

 I venture to think that it will not solve the difficulty to 

 which I have referred, i. e., the unexpected appearance (in 

 certain season) of rare insects, singly or in very small numbers. 



