SCIENCE- GOSSIP. 



2 5 



CONDUCTED BY F. SHILLINGTON' SCALES, F.R.M.S. 



Royal Microscopical Society, April 17th, 

 William Carruthers, Esq., F.R.S., President, in the 

 chair. — Mr. Enock being called upon to give his 

 demonstration on the metamorphoses of one of the 

 dragon-flies (Aesehna cyanea) said that the slides he 

 was about to exhibit were only obtained after many 

 failures. In his endeavours to obtain a complete 

 set of photographs from life which would show 

 every stage in the metamorphosis of the pupa of 

 the dragon-fly, he had taken over one thousand 

 photographs before he was successful. Those he 

 was about to show were taken from the same indi- 

 vidual, and recorded every stage of the process, 

 which occupied a period of six hours only. Con- 

 siderable patience and constant watching were 

 required, as after the first indication of change was 

 noticed the dragon-fly might emerge at any time 

 in the following three days, and when the process 

 of emergence began it went on rapidly — so rapidly, 

 in fact, that three photographs were taken within 

 the space of six seconds. Mr. Enock then showed 

 on the screen photographs of a nymph to illustrate 

 the remarkable movements of the mask by which 

 the insect was enabled to capture its prey. These 

 were followed by a series of about thirty slides 

 illustrating every stage of the metamorphosis, from 

 the pupa to the perfect insect. Mr. E. M. Nelson 

 exhibited a slide of scales of Podwra under polar- 

 ised light, 



Arachnoidiscus Ehrenberc4II. — I have on my 

 microscope stage a slide, mounted by the late Mr. 

 Cole, of the Diatom Arachnoidiscus ehrenbergii, 

 consisting of seven valves grouped without crowd- 

 ing, arranged as six valves around a central one. 

 This is an object well known to most readers of 

 Science-Gossip, but the following particulars may 

 be of interest to some of the younger readers who 

 are fond of the wonder-showing instrument. The 

 seven valves about which I am writing have an 

 average of twenty-two rays, reaching from near 

 the centre to the margin, each interspace being 

 divided some distance inwards from the margin 

 by an incomplete secondary ray. The distance 

 between these principal and secondary rays is 

 again divided by marginal lines still shorter, in 

 some cases two and in others three in number, 

 and these latter by still shorter lines or striae 

 which are placed, with the utmost regularity, on 

 the extreme margin. The hyaline centre of the 

 valve is encompassed by a circle of rods, and this 

 circle of rods is again enclosed by a circle 

 of dots, and from this latter proceed the 

 principal rays. The interradial spaces are 

 occupied by dots, or puncta, that are shown 

 under a high power to be compound, and which, 

 with the power. I am using, present a notched 

 or emarginate appearance. The spaces between 

 the rays are filled by these secondary markings, 

 but they are by no means crowded. They are in 



rows, which are longer, and the elements com- 

 prising them more numerous as we proceed from 

 the centre to the circumference. I have counted 

 these secondary markings in some two or three 

 valves in different sections, and a fair average 

 number will be 85, which multiplied by 22, the 

 number of interspaces, = 1870. This multiplied by 

 7, the number of valves, gives a total of 13,090 

 secondary markings, in addition to the rays, sub- 

 rays, and the before-mentioned components of 

 each valve. I now arrive at my little demonstra- 

 tion of the wondrous power of the compound 

 microscope to afford never-ending interest and 

 delight to the possessor who knows how to use it 

 intelligently, even though he has no object in view 

 but the pleasurable employment of his leisure 

 hours. The above notes were made with a Swift 

 J-inch and the No. 1 ocular, and the slide was 

 placed on a card on the stage, through which card 

 I had made a perforation with a fine sewing 

 needle. The hole was sufficiently large to 

 embrace the seven valves, with a considerable 

 margin to spare. — F. It. BroJtenshire, Exeter. 



Epidermis of Leaf of Auricula. — The 

 glandular hairs mentioned on page 246 of the 

 January Science-Gossip are well worth examining. 

 I have never seen them mentioned in any text- 

 books, and I believe they are not at all familiar 

 objects to microscopists. The slide sent round the 

 Postal Microscopical Society by Mr. McGhie was 

 one given to him by me, and I have never before 

 heard of this object being mounted as a micro- 

 slide. The epidermis of the underside has curiously 

 formed hairs, funnel-shaped, with button-like heads 

 on their points, the broad mouth being downwards 

 to the cuticle. It is difficult to get clean away from 

 the underlying tissue ; but a soak in dilute nitric 

 acid for twenty-four hours will remove it whole- 

 sale, though even then much of the cellular struc- 

 ture beneath is carried away. I have not sufficient ly 

 examined these hairs in the fresh state to express 

 much opinion as to their function. I think it is 

 just probable that these leaves, growing near the 

 ground and having to stand through the wet, wintry 

 weather, secrete an oily substance as a protection 

 to their leaves, both for warmth and to aid in 

 throwing off superfluous moisture. The upper side, 

 being somewhat of a leathery texture, is better 

 able to take care of itself. These hairs are very 

 minute, giving a silvery appearance to the under- 

 side of the leaf, and require a tolerably powerful 

 hand lens for their recognition as hairs. — John J. 

 Ward, Lincoln Street, Coventry. 



Watson & Sons' Holoscopic Objectives. — 

 Messrs. Watson & Sons have sent for our inspec- 

 tion two more objectives of their new " Holo- 

 scopic " series, concerning one of which, a J-inch 

 of N.A. -65, we were able to speak most highly on 

 a previous occasion (S.-G., vol. vi. p 313). One 

 of the new objectives is a i-inch, which we found 

 to be an excellent lens ; but its aperture did not 

 exceed -90, and accordingly it did not show as 

 marked a superiority over one or two other achro- 

 matics of the same power and approximate 

 aperture known to us as might have been expected 

 from its construction. The other objective was an 

 inch of N.A. -30. This was a very fine lens, and 

 fully equal to the high standard Messrs. Watson 

 have set themselves for this series. We may 

 remind our readers that these objectives are con- 

 structed on an entirely new system, with the 



