302 Retrospective Criticism, 



King's College. Although they were exceedingly minute, yet, upon our 

 listening with very moderate attention, their aggregate humming was very 

 distinctly audible. The explanation of this phenomenon, mentioned by 

 White, seems to me to be satisfactorily given by O. (p. 110.). — J.S. 

 Henslow. CambridgCy Feb. 14. 1832. 



We here insert the account supplied by the Rev. L. Jenyns, adverted to 

 above by Professor Henslow. 



All exti'aordinar^^ivarm of Flies. — During the month of September 

 last, a small dipterous insect, belonging to Meigen's genus Chlorops, and 

 nearly allied to, if not identical with, his C. lae'ta, appeared suddenly, in 

 such immense quantities, in one of the upper rooms of the Provost's Lodge, 

 in King's College, Cambridge, as to render the fact worthy of being 

 recorded. The same species of fly, or one closely approaching to it, is not 

 uncommon in most houses, at least in Cambridgeshire, towards the decline 

 of the summer ; but in this instance their numbers were so great, and 

 their appearance so sudden, as to surpass anything of the kind I had ever 

 before witnessed. It was not till after a fortnight had elapsed from the 

 time in which these insects were first noticed that I had an opportunity 

 of seeing them myself, during which interval their numbers had been 

 greatly thinned by fumigations of tobacco and other substances employed 

 as a means of destroying them ; nevertheless, they were still in immense 

 profusion, and my informant told me that in the first instance the greater 

 part of the ceiling, towards the window of the room, was so thickly covered 

 as not to be visible. The exact day of the month on which these insects 

 first showed themselves was not noticed, but, as far as could be remembered, 

 it was about the 17th of September. They appear to have entered the 

 room very early in the morning, by a window looking due north, which had 

 been open during a part of the night, being first observed between eight 

 and nine A.M. A few were noticed in the adjacent rooms facing the same 

 way, although, comparatively speaking, in no great quantity; perhaps in 

 consequence of the windows of those rooms not being opened at quite so 

 earl}' an hour. None at all, however, had been seen in the house previously 

 to that day. We are, at present, so ignorant of the habits and economy 

 of the minuter tribes of insects, that it is not easy to speculate upon the 

 origin of those under consideration. The enquiry which seems most 

 naturally to suggest itself is, whether in the present instance they were 

 all bred in the immediate neighbourhood, and at the same time, or 

 whether they were swarms that had collected from different quarters for 

 the purpose of migration. Many facts are on record which seem to con- 

 firm the idea that insects do occasionally change their quarters in immense 

 bodies ; and some have occurred to myself, which, I have no doubt, were 

 connected with such a circumstance, not only from the large numbers of 

 the insects observed, but from the steadiness of their flight, and their con- 

 tinually persevering in one given direction. It is worth noticing, with 

 respect to the case before us, that King's Lodge is situate close to the 

 river Cam, which at that place runs nearly due north and south, and it is 

 just possible that this circumstance may have had some influence in direct- 

 ing the movements of these insects. I find also, by referring to a journal 

 of the weather, kept in the neighbourhood of Cambridge, that about the 

 time when they were first observed, the wind was N.N.W. and that it had 

 continued fixed in that quarter for four successive days. — L. Jenyns. 

 Nov. 28. 1831. 



Lwninousness of the Sea. — The failure of Mr. Sharpe in detecting these 

 luminous animalcula, as noticed in Vol. IV. p. 506., arises, I conceive, 

 from that gentleman's not being aware of the fact of their being found, when 

 quiescent, only on the marginal surface of the water. I am, in some 

 measure, confirmed in this opinion, by a similar failure on the part of an 

 intelligent naturalist of my acquaintance. The truth is, that being simply 



