Feb. 18, 1886] 



NA rURE 



569 



subject some six years ago. They were published in the 

 not readily accessible Proceedings of the South African 

 Philosophical Society (1879-S0, part iii. p. 161), and were 

 not illustrated by any figure. 



The Singerjie {Platypkura capensis) is a well-known 

 and tolerably abundant insect at the Cape ; and few 

 visitors to the shores of Table Bay can have failed to 

 notice, in the hotter months of the year, the sharp shrill 

 metallic sound produced by the "little singer." It is 

 soon found that the male Cicada alone possesses the 

 power of singing, the female — recognised at once by the 

 long ovipositor folded beneath the abdominal somites — 

 being dumb. If the ventral surface of a male singerjie 

 be examined (Fig. I.) two large ventral cover plates iv.c.p.) 

 are seen, one on either side, meeting in the central line 

 and extending backwards from the metathorax over the 

 anterior abdominal somite. On turning the insect over 

 and looking at the dorsal surface, two very much smaller 

 dorsal cover plates are seen extending forward from either 

 side of the first abdominal somite. If one of these plates 

 be removed with fine pointed scissors, there is seen the 

 wrinkled surface of a thickish chitinous membrane, the 

 drum. Turning the insect over again, so as to examine 

 more carefully the ventral aspect, and removing one of 

 the ventral cover plates, two membranes are disclosed, 

 separated by a transverse chitinous support. Of these 

 the anterior is white, narrow, and opaque, the posterior 

 {p.i'.in.. Fig. II.) translucent, oval, and tightly stretched. 



The transverse chitinous support {ab.st.\) is the sternum of 

 the first abdominal somite ; the membranes are inter- 

 sternal membranes which would seem to be specially 

 modified to act as resonators. The second ventral cover 

 plate may now be removed, disclosing the anterior and 

 posterior resonator membranes of that side ; the anterior 

 resonator membrane of each side may be cut through ; and 

 the abdominal portion of the insect may be separated from 

 the thorax. When this is done there are seen, taking their 

 origin from the mid-line of the first abdominal sternum 

 (Fig. II.,rt/;..f/.i), two muscular pillars (/«.^.), each of which, 

 proceeding upwards and outwards, terminates in a chi- 

 tinous plate, the upper surface of which is, in turn, con- 

 nected by a fine ligament with the drum {dr.). Under a 

 low magnifying power this drum is seen to be strengthened 

 \yith brownish ribs, which, together with its general elas- 

 ticity, cause it to spring back after it has been drawn 

 forward by the action of the muscular pillars, the fibres 

 of which are beautifully striated. Each time the drum is 

 drawn forward and springs back, by the alternate con- 

 traction and relaxation of the muscular pillars, a sharp 

 click is heard, as may readily be proved experimentally 

 on the dead insect. That the well-known metallic sound 

 is produced by a rapid succession of such clicks is put 

 beyond question by the fact that, by irritating the mus- 

 cular pillars in a freshly killed insect, the singing noise 

 may be set agoing, and will then continue for several 

 seconds or even minutes. This I had the pleasure of 



demonstrating to Mr. Roland Trimen, F.R.S., curator of 

 the Cape Town Museum, the abdomen singing merrily 

 when the head and thorax had been pitched out of 

 window or destroyed. A weak current of electricity 

 would also cause the singing to commence. The sound 

 generally ceased after a while in a few isolated clicks, and 

 at that time the waves of contraction in the muscular 

 pillars were plainly visible. The singing noise was less 

 sharp and clear than in the living insect, owing probably 

 to the disruption of some of the resonator membranes ; 

 and I have noticed that rhythmical motions of the abdo- 

 men in the live insect produce rhythmical alterations in 

 the intensity of the sound. The cover plates are doubt- 

 less mainly for protection ; but the fact that on their 

 removal the sound is less full and intense shows that they 

 also may play the part of sounding-boards. 



Fig. II. is a slightly diagrammatic view of the severecl 

 abdomen as seen from the anterior end. ab.st\ and ii 

 are the sterna of the first and second abdominal somites ; 

 p.r.m. the posterior resonator membrane stretched between 

 them ; v. in. a vertical membrane ; m.p. the muscular 

 pillars ; dr. the drum ; and d.c.p. the dorsal cover plate of 

 the right side, that of the left side being removed. 



I may mention, by way of appendix, that in this species 

 the rostrum contains only three stylets ; two lateral, 

 toothed on their external edges ; one central and smooth. 

 Although this central style shows, in some cases, indica- 

 tions of its having arisen by coalescence of two lateral 

 styles, it is distinctly one and indivisible. 



C. Lloyd Morgan 



University College, Bristol 



RADIANT LIGHT AND HE A T '■ 



V. 



Evidence awarded by the Spectroscope as to the Nature of 



the Elements 



THE point of greatest speculative interest connected 

 with our subject is perhaps that regarding the con- 

 stitution of the so-called elements. 



What light, it may be asked, does spectrum analysis 

 throw on this vexed question ? Does it lead us to imagine 

 that these bodies are truly elementary ? Or to believe 

 that they are in reality compounds which might be broken 

 up if we had sufficiently powerful instruments for this 

 purpose at our disposal ^ 



I shall begin my remarks on this subject by taking it 

 for granted that the constitution of matter is atomic and 

 molecular. 



When, therefore, two chemically different substances 

 combine together we have the union of two heterogeneous 

 atoms, forming a molecule of the compound substance. 

 Thus, when an atom of chlorine and one of sodium com- 

 bine together we have, as a result of the combination, 

 chloride of sodium or common salt, and an ultimate 

 molecule or compound atom of chloride of sodium may 

 be described as the smallest portion of that substance 

 which possesses all the properties of common salt, and 

 which, if divided further, would be split up into one atom 

 of sodium and one of chlorine. 



The molecules of bodies are very frequently so placed 

 as to have an attraction for each other, under the influ- 

 ence of which the body assumes a solid, or, it may be, a 

 liquid state. 



Sometimes, however, we have the body in the state of 

 gas, in which the various molecules are so far apart as to 

 have no perceptible attraction for each other. It is by 

 means of such a gas that we can best study the properties 

 of molecules as far as radiant light and heat are con- 

 cerned. Now, spectrum analysis uni|uestionably tells us 

 that at comparatively low temperatures and great near- 

 ness of particles we have a comparatively complicated 



^'Continued from p. 254. 



