2IO 



SCIENCE- GOSSIP. 



This was a curious projection on the extremity of 

 the palpus, free to move in all directions, even 

 inwards. It is not found on the common gnat, but 

 is seen on the palpi of ticks. Coloured drawings 

 were also shown. Mr. Eousselet exhibited a slide 

 of Zop7t,opiis crystallinus, beautifully mounted by 

 himself, and Mr. Earland exhibited a slide showing 

 trifurcate sponge spicules. 



Manchester Microscopical Society. — The 

 monthly meeting of this Society was held on 

 Thursday evening, November 7th, at the Grand 

 Hotel, Manchester. Mr. Mark L. Sykes, F.E.M.S., 

 read a paper on " Evolution in Butterfly Scales." 

 Mr. Sykes said that he had selected for the purposes 

 of his communication some of the specimens illus- 

 trated in his paper on " Natural Selection in the 

 Lepidoptera," published in the " Transactions" for 

 1897, as the illustrations would be available to the 

 members, and would enable them to see the close 

 resemblances which these butterflies bear to one 

 another. In whatever direction the mimicry may 

 tend, whether in simulation of inanimate objects 

 such as leaves or twigs or moss, for concealment 

 from their enemies on the one hand or to enable 

 them to secure their prey on the other, in mimicry 

 of conspicuously marked or highly coloured in- 

 edible by edible species, in resemblance between 

 two or more equally distasteful but entirely different 

 species, or whatever purpose the mimicry may 

 serve ; it seems that the resemblance is in outward 

 appearance only. Although the similarity in 

 colour, pattern, and markings may be so close as 

 to be almost identical, microscopical examination 

 of the wing scales of these insects shows that the 

 details by which the likenesses are brought about 

 .may be, and often are, widely different. The 

 specimens from which the examples were taken 

 fall under two groups of mimicry, that of Midler 

 and that of Bates. The Mullerian form of mimicry 

 is that in which two or more highly coloured, con- 

 spicuously marked, or peculiarly shaped butterflies, 

 all inedible and distasteful to the insect-eating 

 animals, are so closely alike as to be easily mistaken 

 one for the other. These by their similarity in ap- 

 pearance afford each other mutual protection by 

 dividing between them the total number destroyed 

 by the young Insectivora of each season in learning 

 what is and what is not good for food. The 

 Batesian mimicry is that in which certain con- 

 spicuous and nauseous species that the young 

 birds, etc., quickly learn are distasteful, are simulated 

 by others which are not nauseous, but which have 

 acquired the colour-markings of inedible forms and 

 are thereby protected. Amongst the former are 

 the Heliconinae, Danainae and Acraeinae, all of 

 which include amongst their members numbers of 

 highly-coloured species conspicuous for their 

 markings in red, yellow, black and blue, with 

 intermediate tints or shades, and. which are easily 

 distinguished in their surroundings. In the latter 

 are included butterflies of nearly every sub-family, 

 and some of the diurnal moths, and both are found 

 nearly all over the world. Yet, on examining with 

 the microscope the scales of the wings of these 

 mimetic butterflies, it will be found that, so far 

 from the similarity in superficial appearance being- 

 similarity in detail and pattern, there is a wide 

 diversity in scale structure and arrangement. The 

 scales vary not only in numbers, but in size, colour, 

 and form, and this is the case even where one 

 inedible species mimics another. Mr. Harry Yates 

 exhibited under a number of microscopes tow- 



nettings from various localities, chiefly Naples, 

 Port Erin, and Stromness. The results of these 

 gatherings, collectively termed plankton, he said 

 differed very much according to locality and time 

 of the year. The state of the weather may also 

 account for the presence of specially abundant 

 species. The young stages of nearly all forms of 

 marine life are to be found in floating condition, 

 at the mercy of tides and currents, thus spreading 

 the species over wide areas. 



C. Baker's Engineering Microscope.— This 

 instrument (fig. 1) has been specially designed for 

 the examination and photography of metals (see fig. 

 2). It contains several distinctive characteristics. 

 As it is intended for the examination of opaque 





Fig. 1. Engineering Microscope. 



objects exclusively, no means of snbstage illumina- 

 tion is provided, and even no stage aperture. 

 Opaque objects to be examined with moderate 

 powers can be illuminated in the ordinary way by 

 means of a bull's-eye, a side reflector, or a lieber- 

 kiihn, but with high powers a vertical illuminator 

 must be used. This is simply a collar placed above 

 the objective with a small hole at the side through 

 which a strong light from the lamp is directed, the 

 size of the hole being adjusted by means of a dia- 

 phragm. Within the collar is a disc of cover-glass 

 set at an angle of 45°, which without materially 



