78 3Ir. F. A. Dixey [March ?., 



stance which constitutes the outer covering, or external skeleton, as it 

 is called, of many insects, and which when met with in Inilk is of a 

 hard and horny consistence, as may be seen, for instance, in the fore- 

 wings or " elytra " of beetles. Chitin is practically a dead material, 

 and there is no trace to be found in the scale of any protoplasmic or 

 living matter. The granules which are present are probably pigment 

 granules, the presence of which in the ordinary scales imparts to the 

 wings their characteristic colour. So far we have discovered no ap- 

 paratus to which we may attribute the production of perfume. 



But now let us examine the means by which the scale is attached 

 to the membrane of the wing. The point, or rather surface, of 

 attachment is the accessory disc, which fits into a cup-shaped depres- 

 sion in the wing-membrane, which cavity, however, is generally not 

 large enough to admit the whole of the disc. In many species can 

 be seen an orifice in that part of the disc which is enclosed, when the 

 scale is in situ, within the cup-shaped cavity or socket just men- 

 tioned. And when the fimbrise are examined with a very high 

 power, an appearance is seen in many species which suggests that 

 their free extremities are not closed, but open ; that they are, in fact, 

 minute tubes which put the interior of the scale into communication 

 with the outer air. Noav, can we discover any means by which, say, 

 a vapour entering the disc by the orifice in its buried portion can 

 be conveyed through the scale and find its way out through the 

 patent extremities of the firabrite ? It certainly appears that we 

 can. Within the disc there is generally visible a chitinous structure 

 which often bears the appearance of a convoluted tube ; the foot- 

 stalk which forms a bridge between disc and lamina is apparently 

 not solid, but pervious. The lamina itself consists of two delicate 

 chitinous layers, one of which may be called dorsal and the other 

 ventral, enclosing a flattened cavity which contains a certain amount 

 of interstitial material. This latter takes various forms in different 

 species, but very often presents the appearance of a longitudinal 

 striation, which in all probability betokens the existence of fine 

 -parallel channels or passages traversing the interior of the lamina 

 side by side from base to apex. This longitudinal striation is fre- 

 quently obscured by the accumulations of granular pigment ; but in 

 many cases there is a comparatively clear area near the apex where 

 the striie can be fairly well made out, and where they can be seen to 

 correspond in number and position with the individual fimbriae. 

 There is, then, much reason to suppose that the caA'ity of the lamina 

 is more or less completely divided into channels which communicate 

 in one direction with the fimbri;\3, and so, through the orifices of the 

 latter, with the outer air ; and in the other direction through the 

 footstalk with the disc, and so through the aperture of the disc with 

 the socket of the wing-membrane and its underlying structures. We 

 have, therefore, some warrant for considering the scale to be a piece 

 of apparatus not indeed for the manufacture, but for the distribution 



