118 THK KNTOMOLOGI8T. 



the neglect of this combination of observation which has contri- 

 buted in no small degree to some of the curious errors so often 

 met with in accounts of the life-histories of even our commonest 

 insects; such as, for instance, in the egg-laying of the Dytisci, a 

 genus of carnivorous water beetles, where, in many text-books, 

 you will find it definitely stated that the female extrudes her 

 eggs at random in the water. This assertion was founded in the 

 first place on the experience of L3^onnet, whose captive beetles 

 thus oviposited, as pent-up insects are wont to do ; whereas 

 under natural conditions the eggs in this genus are really de- 

 posited singly and with circumspection in the submerged portions 

 of various rusbes, pond-weed, and other aquatic plants, and for 

 the careful placing of which the ovipositors of the females are 

 provided with two sharply-edged plates, one on either side of the 

 oviduct, with which incisions are made in the submersed stems 

 to receive them. This tendency to promiscuous oviposition dur- 

 ing captivity I have often noted in connection with Dytiscus 

 punctulatits, Gastroidea viriduUts, and other insects. 



Whilst speaking of the Dytisci, I will here call attention to 

 one or two of the simpler problems awaiting solution, to which I 

 just now alluded. Those of us who have kept Dtjtiscus jnincttilatus 

 or D. mnrginalis alive for any length of time will have become 

 cognisant of the fact that, in common with many other imagines 

 and some few larvse, they stridulate at times with great energy. 

 This stridulation is produced in two distinct tones — the one 

 harsh and shrill, the other a lower " trill" or buzzing sound. 

 We shall moreover have probably remarked that such notes are 

 almost invariably emitted towards nightfall or during the evening 

 hours, and I am strongly inclined to the opinion that the Dytisci, 

 like the Gyrini, or " whirligig " beetles, are in the habit of 

 stiidulating previous to flight ; for, in so far as my own experience 

 goes, these musical efforts are confined to the evening, during 

 which period, too, the beetles fly. But the question to which I 

 particularly wish to direct your attention is, by what mode are 

 these sounds generated 9 The only definite statement I can find 

 on the subject is by Prof. Miall, who says " the sound is produced 

 by rubbing the under side of the wing-cases against the ends of 

 the body"; but if these areas are examined stridulating organs 

 are not readily perceptible. The fact that Mr. C. J. Gahan made 

 no reference to the Dytisci in his exhaustive paper " On the 

 Stridulating Organs in the Coleoptera," read before the Entomo- 

 logical Society of London during the session just closed, prompted 

 me to write him on the subject, with the result that he tells me 

 he has never been able to detect the presence of stridulating 

 organs in the genus. "Whether they make the sound in the 

 manner described by Prof. Miall or not," he proceeds, " I cannot, 

 of course, say, but I am inclined to doubt his statement. There 

 is nothing on the elytra or abdomen at all resembling the stridu- 



