• KNOWLEDGE 



[Jan. 2, 1885. 



•wistful Datchery, ia " some Jetective employed by Grew- 

 gious." (Imagine a wistful Jetective !) 



Thougli Dickens said to Miss Ilogai-tli (who unquestion- 

 ably was the only person to whom he would have commu- 

 nicated anything near his real ideas) that he feared '■ the 

 Datchery assumption" (even what he had already written 

 about it) might explain the mystery, " H. L." insists that 

 there is no assumption at all (foi- if Datchery is "some 

 detective " what assumption is there '!), and that the 

 character, so far as dealt with, throws no light at all on 

 the mystery, — unless " H. L." considers A/s interpretation of 

 Datchery self-luminous. 



Though Dickens flatly told Forster that he would not 

 communicate the real idea of the mystery, " H. L." will have 

 it that what Dickens said to Forster immediately after- 

 wards, was the real solution. 



" H. L." believes that Dickens communicated to Fildes the 

 true end of the story, though it is well-known he never 

 gave Hablot Brown or Marcus Stone the least inkling of 

 the true end of any of the stories they illustrated. 



The figure in the tomb from which Jasper shrinks back 

 apjialled in the suggestive jiicture at the foot of the 

 nuraher-cover is not Edwin Drood, but Neville playing 

 bogey. " H. L." would admit, I suppose, that the figure 

 was meant to terrify Jasper by its resemblance to Drood, 

 yet there is Jasper with a lantern, apparently of e.v;cellent 

 quality, staring hard at the face of the figure, and yet 

 " H. L." thinks, conceivably mistaking Neville's face for 

 Drood's, though the two were as unlike as they could well 

 be.* 



If " H. L.'s " ideas are correct, the " Mystery of Elwin 

 Drood " is flat, stale, and unprofitable. But let any who 

 have not read the story, or having read it have not sus- 

 pected that Drcod really escaped and returns as Datchery, 

 go through the half-written story with this interjn-etation 

 in view, and I fancy they will find the incomplete novel 

 more interesting than many fine novels which have been 

 written out to the end. It was to sugjest this that Mr. 



Foster wrote his article. 



THE ENTOMOLOGY OF A POND. 



By E. a. Butlee. 



ABOVE THE SURFACE (continued). 



\NOTHER of the Hydrocampidte, called Catachjafa 

 hmnalii (Fig. 1) is very common over ponds in 

 which duckweed abounds. It is a small whitish insect, 

 with the edge of its hind wings adorned with what looks 

 like a row of tiny sparkling diamonds set in a band of jet. 

 Its larva is a little black fellow with velvety skin ; it feeds 

 on duckweed [Lemna), and, as usual, inhabits a case 

 covered with the leaves of its food-plant, but, unlike the 

 Hydrocampas, the case needs to be made of more than two 

 pieces, on account of the minute size of the leaves. It is 

 of an irregular oval form, about half an inch in length, and 



troth than she imaginecl. A careful and appreciative reading will 

 give better results. 



* Dickeng, we know from a dozen similar cases, would have had 

 no difficulty in exjilaining why Jasper failed to recognise Drood on 

 the one occasion when he had an opportunity of seeing him close at 

 hand. A real change of appearance might well have followed six 

 months of slow recovery from the effects of the attack, &c. This, 

 and the disguise (the voice also being altered), would suffice to 

 prevent Jasper from even imagining that Datchery was the man 

 ho supposed he had not only slain but gotten rid of utterly. Th.it 

 Datchery had passed through an ordeal is evident from what he 

 says after his meeting with Jasper. It would have been no ordeal 

 for " some detective." 



rather less than half as much in breadth : the leaves of 

 which it is composed are laid so as to overlap, and at the 

 two ends some of them hang down over the openings, so 

 that when the little hermit is within its cell, one can hardly 

 distinguish the case from a mere accidental collection of 

 duckweed leaves, such as may so frequently be met with. 

 The late Mr. W. Buckler, who devoted his time with 

 remarkable assiduity to studying, describing, and figuring 

 the preparatory stages of many Lfpidoptera, found that a 

 larva of the present species, when deprived of its case, took 

 only .six minutes to put together the leafy framework of 

 another, inside which it remained for a time invisible, 

 apparently busy in finishing it off with a neat lining of 

 silk. Its body is apparently impervious to inoi.sture, for 

 after submergence for any length of time, it comes up to 

 the surface as dry as when it went down. Like the 

 Hydrocampas, it hibernates during the winter months, and 

 begins to feed again in the warmest days of April, the 

 perfect insect appearing in May and June. It pupates in 

 its larva case, and after the issue of the moth, the old case 

 is found to contain both the last cast skin of the larva, and 

 the empty and broken pupa case. 



The caterpillars of the three insects already mentioned, 

 though living beneith the surface of the water, are not 

 provided with any means of subaqueous respiration ; they 

 are furnished with the ordinary spiracles, and breathe air 

 directly in the usual manner, and the tiny globules of air 

 that hang about the margins of the spiracles like so many 

 silvery beads and streak,=, look very pretty on the sooty- 

 black body of Ciitadi/sta. But the larva of Paraponyx 

 stratioialis, a brownish moth much like a Hydrocampa, 

 besides its spiracles, is possessed of organs similar to those 

 we have so often referred to before, through the thin walls 

 of which the air dissolved in water can diffuse into the 

 trachea' with which they are furnished. These organs are 

 usually called " tracheal gills," a not very appropriate name, 

 iua'?much as a gill is properly an organ to which the blood 

 is conveyed in great quantities, there to receive the revivify- 

 ing action of the oxygenated water that passes over it ; but 

 in this case, the gas is conveyed to the blood throughout the 

 body, instead of the blood to it. 



Fig. 1. — Cataclysta lemnalis. 



The last and most remarkable species of the family is 

 one that we have had occasion to mention once before — 

 Acenti-opus nivetts, noted as having been for a time a bone 

 of contention between entomologists, the questions in debate 

 being, first, whether it was a moth or a caddis-fly, second, 

 admitting its lepidopterous character, whereabouts in that 

 order it was to be located, and third, whether there was 

 more than one species. It is a small, whitish insect, which 

 appears in July, and is nocturnal in habits. During the 

 daytime it sits about on weeds, sticks, boards, &c., close to 

 the water's edge, and is very sluggish, not taking to wing 

 unless disturbed. But just about dusk its spirits revive, 

 and it starts on its nocturnal peregrinations, skimming 

 about in broken circles so close to the surface of the water 

 as to seem to be actually swimming; while flying, it 

 scarcely ever seems to leave the surface, but, every now and 



