Feb. 12, [885] 



NA TURE 



34i 



use of exhibitors. Besides the engine which supplied 

 power in the machinery gallery last year, an engine is 

 being erected in the new gallery which is being put up 

 along the north side of the old South Gallery, as described 

 in the Journal of the Society of Arts for January 30. A 

 third engine will also be provided, which will drive 

 machinery in one of the Foreign Courts. It will thus be 

 seen that those visitors who have mechanical tastes will 

 be amply provided for. 



As regards the prospects of applied chemistry, we are 

 not able to speak so confidently. Probably the complete- 

 ness of this portion of the show will almost entirely depend 

 on the success of the efforts which are being made by the 

 Society of Chemical Industry to secure a collective exhibit. 

 The announcement made by the executive at the outset, 

 that it was desired to show processes rather than products, 

 is believed to have kept back many manufacturers from 

 seeking to show specimens, while it is obvious that but 

 few chemical processes could conveniently be carried on 

 in an exhibition gallery. Possibly this rule might have 

 been abrogated as regards the chemical section, and we 

 believe that no attempt will be made to enforce it with 

 reference to the collection of the Society of Chemical 

 Industry, in which it is proposed that the information 

 required shall be given by means of a collection of pic- 

 torial diagrams, exemplifying some of the more interesting 

 or more important chemical operations. 



As our readers are aware, a similar work is being under- 

 taken by the Physical Society in the class devoted to 

 " Philosophical Instruments and Apparatus," though in 

 this case there will be less left for the society to do, since 

 the principal makers of apparatus have come forward in 

 sufficient numbers to ensure a good representative collec- 

 tion. The object, however, of the Society in exhibiting 

 has been not so much to supply deficiencies, as to show 

 the work which has been done by its own members. We 

 believe that the Kew Observatory and the Meteorological 

 Society will also be among the exhibitors, the latter in 

 their old place in the grounds. Besides this, a very 

 interesting exhibit is promised — namely, a fully fitted 

 observatory, which we understand one of our best known 

 makers had offered to fit up. 



In the class devoted to Photography, which comes next 

 both in the classification and in actual position in the 

 galleries to the philosophical instruments, the Photo- 

 graphic Society has undertaken to form a collection of 

 apparatus and specimens not likely to be shown by 

 makers. It appears that the Society intend to go a little 

 beyond the precise limits of the Exhibition, and to show 

 a collection of examples illustrating the entire progress of 

 photography from the inventions of Niepce and Daguerre, 

 and it may doubtless be assumed that in so special a case 

 no objection will be raised, especially as but a very small 

 space indeed, and that only on the walls, will be required 

 for what cannot fail to prove a most instructive and 

 interesting collection. 



The progress which has been made in electric lighting 

 has indeed been sufficiently illustrated in the exhibitions 

 of last and of the preceding year ; in fact, the Health 

 Exhibition offered almost the only public example of any 

 progress at all in England. Doubtless the lesson will be 

 repeated this year, and on a more extended scale, for we 

 learn that considerable additions are being made to the 

 arrangements for electric lighting of the buildings, while 

 it is intended to use the light also for the garden illumina- 

 tions, an improvement due to the energy of Sir Francis 

 Bolton. If this idea is carried out on the plan which we 

 understand is intended, the instantaneous lighting up of 

 the myriad incandescent lamps by which the gardens are 

 to be illuminated will certainly be one of the most 

 popular, and one of the most wonderful, sights in London 

 next summer. 



The above remarks refer only to the English portion 

 of the Exhibition. How much will be contributed by 



foreign countries it is not yet possible to ascertain. 

 Thanks doubtless to the efforts which were made by 

 certain of the members of the British Association who 

 were in the States last year, the American Court promises 

 to be well filled, and it must be admitted that in the 

 present Exhibition, if we get American ingenuity well 

 represented, we shall not very greatly miss the contribu- 

 tions of other countries, though we hope, all the same, 

 that these will not be lacking. 



THE RETINA OF INSECTS 

 T T might have been thought impossible for any one who 

 *■ has studied the eyes of Arthropods to doubt that the 

 so-called retinulas are really the nerve-end cells of the 

 eye, and correspond with the rods and cones of the verte- 

 brate eye. The evidence in favour of this view accumu- 

 lated by the researches of almost every observer, including 

 such eminent authorities as Johannes Miiller, Leydig, 

 and Grenadier is so overwhelming that of late years no 

 one has thought fit to dispute it. 



Mr. Lowne has, however, at last attempted to overthrow 

 this theory, and in a paper just published in the Trans- 



ffwtl 



-. t/ 1 "* 



Fig 



1. 



Fig 2 . 



'•■ 1. — Section through the eye of Squilla, showing ' the distribution 

 of the ultimate nerve fibrils to the retmula;. The Ommatidia to the 

 left of the figure are drawn with their accompanying pigment cells (/ g) 

 complete ; in the three to the right these are omitted in order to 

 show more clearly the distribution of the nerve fibrils ; tr, corneal facets ; 

 c.c, crystalline cone : r/t, rhabdom ; ?; retmula ; /' "■', basilar mem- 

 brane ; t.a, terminal anastomosis of optic nerve fibrils supplying the 



i through the ommatidium of Squilla, showing the 

 rounding the central rhabdom. The retinula: are 

 seen to possess a considerable amount of granular pigment, which is un- 

 evenly distributed in the different cells. 



actions of the Linnean Society, vol. ii. part ii., on "The Com- 

 pound Vision and the Morphology of the Eye in Insects," 

 has brought forward certain statements to prove that all 

 the parts of the eye in front of the basilar membrane 

 are dioptric, whilst the true (?) retina is situated behind it. 



To one who has been devoting considerable time and 

 attention to the eye of Arthropoda, this proposition is 

 particularly striking and unexpected, and many points 

 at once occur which show that it is untenable. 



In the first place it is untenable because we have ample 

 evidence to show that the original theory is the true one. 

 The nerve-end cells throughout the animal kingdom have 

 certain definite characteristics. They are the cells in 

 which the ultimate fibrils of the optic nerve terminate, 

 and no nerve fibrils have ever been seen to leave them to 

 supply other parts of the eye ; and, in the second place, 



