January, 1915. 



KNOWLEDGE. 



25 



The development of the wings takes place in later stages, 

 and can be easily identified on the second and third thoracic 

 segments as dark ridges or plates : they result from the 



Expansion takes place, and this is due to the injection 

 of fluid into the \-eins ; the latter spread further and further 

 apart, the folds becoming effaced : this takes about fifteen 



upward growth of the pleura of the meso- and metathorax. 



In the final stages long wings appear, and the antennae 

 consist of seven segments. 



The transformation of the n\Tnph into an adult insect 

 provides an interesting opportunity' for observations, and 

 can be watched, o\\-ing to its occupying some time. The 

 change takes place out of the water, and the nymph seeks 

 out some support, such as a branch or stem of a plant, 

 several feet away from its former home, viz., the pond. 



The eyes of the n\Tnph, within a very short period, 

 undergo a remarkable change, and become bright instead 

 of dull, whereas, in the early stages, they seem to appear 

 opaque, owing to the pressing close to the sockets of the eyes 

 of the Fly. 



The plant is grasped by the two hooks on the legs (see 

 Figure 21), and it holds on firmly with its body in a vertical 

 position ; when fixed close to the stem internal changes take 

 place. 



In about ten minutes after drying, the thoracic skin 

 sphts, and the thorax of the fully formed Fly becomes 

 \-isible through this opening. 



The new thorax swells visibly, and, acting as a wedge, 

 helps to enlarge the opening, which soon extends to the 

 fore edge of the thorax ; then it splits along the neck, 

 and, finally, to the level of the eyes. At this point lateral 

 openings proceed on either side. 



The head becomes distended and completely withdrawn, 

 appearing so large that one has great difficulty in beUeving 

 that it was enclosed in so small a space previously. 



When the head and thorax become free, the legs are 

 carefully drawn out of their sheathr ; and to assist this 

 process the Dragon-fly, when emerging, bends backward until 

 the whole body length is held only bj' the hindmost segments, 

 which still remain enclosed in the larval skin. 



The whole insect hangs, with six segments of the abdomen 

 exposed — these segments are wet and limp — from the dry 

 n>Tnph skin, still clinging to its support by its stiff and empty 

 legs. 



In less than half an hour the body becomes arched 

 considerably by the sudden spring of its whole length in 

 the opposite direction, and the empty n^miph skin is seized 

 by the legs, which hold on to the sides of the opening 

 firmly. The hinder part of the body, consisting of the 

 remaining four segments of the abdomen, is withdrawn, 

 and the insect hangs by its legs only. 



At this stage the emerging insect appears to be some- 

 what deformed, and the abdomen is not quite so long as that 

 of the insects already flying in the fields. 



The wings, which seem to be very large when compared 

 with their size, when enclosed in their nymph skin are turned 

 edgewavs, folded like a fan along their length, and- trans- 

 versely, thev at once begin slowly to expand. At first they 

 appear dull and mealy-looking, but, as they lengthen, a 

 flatter and clearer look results, until in about thirty minutes 

 they show aU the beaut\' of their gauzy outline, but are 

 still pale green and soft, like the body. 



As the fluid which fills the insect is exuded, drop by drop, 

 the limp appearance vanishes, and the body stiffens and 

 becomes dry. 



The wings also dry, and become placed in their final 

 position, but are not spread out ; for though they afterwards 

 become stiff, and as firm as talc, they are still wet, and soft 

 as paper. 



* " Natural Historj' of .Aquatic 



minutes, and at the same time the abdomen is gradually 

 lengthened. 



It is more than two hours before the wings can be 

 spread horizontally, and from two to three hours more before 

 they can support the weight of the body. 



When first emerged the Dragon-fly is ven,' faint in colour, 

 but its brilliancy and distinctions of colouring gradually 

 increase.* 



WTien the wngs and body have dried and hardened, the 

 insect starts away swiftly on a level course, wheeUng 

 sharply to the left or the right, and backing with ease and 

 facility. 



In the pond the nymph preyed on other aquatic inhabit- 

 ants, and now in the air winged insects form its prey. 



Figure 18 {Aeschnura cyanea) shows the insect with a 

 Dipteron held in its jaws. This was obtained by one of 

 our well-known authorities on the Odonata (Dragon-flies) 

 and kindlj' lent to the writer. 



W. Harold S. Cheavin, F.R.M.S. 



CORRIGENDUISI.— In the December issue (Volume 

 XXXVH), page 434, the descriptions of Figures 420 and 

 421 were interchanged. 



THE QUEKETT MICROSCOPIC.\L CLUB— At the 

 five hundred and second ordinary meeting of the Quekett 

 Microscopical Club, held at 20, Hanover Square, W., on 

 November 24th, the President (Professor Arthur Dendy, 

 D.Sc, F.R.S.) first called upon the meeting to pass a reso- 

 lution expressing the members' deep regret at the loss they 

 had sustained by the death of Doctor M. C. Cooke, 

 .M.A., LL.D., A.L.S., which occurred on November 12th, 

 at his residence in Southsea. 



Dr. Cooke, knowm as the " Father of the Club," was one 

 of the eleven members who attended the preUminarj' meeting 

 of the Quekett Microscopical Club held on June 14th, 1S65, 

 and he was elected one of its first Vice-Presidents. He was 

 President in 1882 and 1883, and was elected an honorary 

 member in 1893. 



Mr. J. Grundy introduced and explained the great 

 advantages of a micrometric table by Mr. E. M. Nelson. 

 Tills table, pubhshed by Messrs. H. F. Angus & Co., 83, 

 Wigmore Street, London, W., price 3d., contains full par- 

 ticulars relating to its use. Its utihty is that, having taken 

 the reading from the eyepiece micrometer and that of one 

 division of a stage micrometer in the di\isions of the 

 eyepiece micrometer, on reference to the table, the size 

 of the given object is obtained at once without any further 

 calculation. At the conclusion of Mr. Grundy's lucid 

 explanation, Mr. AinsUe, R.N., concurred as to the utihty 

 of the table. 



Mr. D. J. Scourfield, F.R.M.S., read a paper upon a 

 new Copepod found in water from hollows in tree-trunks. 

 He stated that in recent years, o-\\'ing to endeavours to 

 discover the life-histories of mosquitoes and other insects, 

 supposed to be connected with the dissemination of tropical 

 diseases, much attention has been given to the subject 

 of the little animals found Uving in the water of these 

 httle hollows. According to a recent paper pubUshed by 

 Picado no fewer than two hundred and fifty species of animals 

 have been found living in this peculiar environment, 

 forty-nine being new to science. They belong to almost 

 all groups of invertebrates, but naturally insects and their 

 larvae predominate. 



Insects," Miall, pages 340-45. 



