246 



KNOWLEDGE 



[No\'EMBER 2, 1896. 



band, a mark easily distinguishing this beautiful species 

 from all its congeners. 



On approaching from the sea any open sandy shore in 

 the Isle of Cuba a copse wood is perceived, above the coral 

 reefs, forming a close and nearly impenetrable belt, maybe 

 ten or twenty yards wide, and composed of almost one 

 kind of tree, of aspect strange to the European eye, the 

 Coccolohii uiiferii, the so-called I'lvro of the Spaniards. 

 Immediately behind this belt an immense variety of 

 vegetation grows in the parched sand, the plant of chief 

 interest to us being that technically titled Ompluih'a 

 tridihlrii. 



This, the Cob or Hog nut of .Jamaica, the .Iri'llinmol the 

 Island of Cuba, sometimes reaches the dimensions of a 

 tree fifteen feet high. The part that concerns us is the 

 leaves— great, thick, heart-shaped things of leathery 

 texture, and a scabrous surface of a pale green ; the 

 young leaves and the leaves of the young plants, although 

 of the same texture and colour, are of different form, being 

 deeply incised. 



During the heat of the day, on the upper side of the 

 mature entire leaves of this tree the caterpillar of I'. Loi.i- 

 (luralii may often be discovered torpidly reposing, screened 

 from the fierce rays of the sun within a thin transparent 

 silky web. At night, no longei sluggish it quits its cover, 

 greedily stripping (hnjihuten of its foliage, so that trees are 

 left with scarcely a single leaf ; nor is it inactive in the day- 

 time when disturbed, but can run about quickly, and shows 

 little affinity to the caterpillars of other diurnal Lfpidoptira, 

 which usually have a slow motion. 



In February, and the ensuing months of spring and 

 summer, the perfect insect deposits its eggs on the tender 

 incised leaves, laying them singly. The young larva is of 

 a pale green, with a yellowish head; but ere it reaches 

 maturity its appearance undergoes considerable alteration. 

 It is then about two inches long, and moderately hairy ; 

 and while the body varies in tint from a pale yellowish 



Vrniiia leilus. Two-tliirils natural size. 



green to a tlesh colour, the head now is red, irregularly 

 sprinkled with some black spots, and the prothorax of a 

 velvety black. The head is polished and sessile. But these 

 larvip difi"er much from each other in size, marking, and 

 colour, more so than ordinarily occurs with larva- of the 

 same species. 



Eventually the larva spins an oval cocoon of dirty 

 yellow silk, of which the threads are so few, and so loose, 

 as to allow the inmate to remain visible through the 

 meshes ; within the cocoon it changes to pupa. The 

 chrysalis is not at all angular, and, moreover, reposes in a 

 horizontal position. Yet it agrees with that of most 

 diurnal Lepidoptera in being rather gaily coloured. 



The flight of the imago is truly diurnal, swift, always 

 strong, and in starts. The interior of the island it does 

 not seem to haunt, but may be found plenteously in 

 gardens at a distance of two, and even three, leagues from 

 the shore. But it is by far the mo=it common near the 

 sea, because there grows its favourite (hnphnlcit. As a 

 matter of fact, however, it prefers flitting about the leaves 

 of the Coccolohd urifi'ra, unless when employed in depositing 

 its eggs. 



As the genus ihiiiihalcn is common in Brazil and 

 (luayana, in all probability it affords pabulum to Vrania 

 hrnsilii'nsi.i and ' . hilus, species whoso habitats are Brazil 

 and Cayenne and Surinam respectively : for, as MacLeay 

 remarks, "the minor natural groups of LrpiilopteiK often 

 keep very constant to the same natural group of plants." 

 In a word, the gorgeous Madagascar Cliri/slridin madatjas- 

 rarensis, the Species of the East India isles, and many 

 more, may likewise feed on leaves of seaside F.uphorhiacece. 



Eemark the habit of thefe day-llying moths of perform- 

 ing migrations. The very beautiful /'. fid<iniH migrates 

 annually, from east to west, in August and September, 

 across the Isthmus of Panama. Flights have been 

 observed by a naturalist in the Isle of Caripi, near Para, 

 in the Brazils, at Pernambnco, at Ilio Janeiro, and in the 

 Southern States; but he saw them nowhere so abundant as 

 on the Amazons. From early morning till nearly dark 

 the insects passed along the shore in amazing numbers, 

 but most numerously in the evening, and mainly from west 

 to east. Swainson, speaking of ''. lirasilicnsis, a species 

 almost the exact counterpart of V. leilus, states that he 

 witnessed a host fiying during the whole of a morning in 

 June past Aqua Fria (Pernambuco), in a direction from 

 north to south — not one deviating from this course, not- 

 withstanding the dowers that were growing around ; and 

 though they Hew near the ground they mounted over 

 every tree or other high object which lay in their path, 

 and it was impossible to capture a single specimen, so 

 rapid was their flight. For three or four days they 

 continued to pass in this manner. On the occasion of the 

 flights over the city of Panama, iu some cases the insects 

 are attracted into houses by the light, so as to almost fill 

 the rooms. At night they are accompanied by goat-suckers, 

 and during the day by swallows and swifts, which probably 

 destroy large numbers. As will be gathered, these 

 migrations of Irania, though regular, are confined to 

 comparatively narrow limits in the tropics. 



THE SPECTROSCOPY OF ARGON. 



M 



Translated from the French, ivith Additions, 



By T. L. Alger, LL.D., Ph.D. 



H. CROOKES found, on examining this gas with 

 a very powerful spectroscope, that it gives, like 

 azote, two distinct spectra, according to the 

 intensity of the induction current employed, 

 hut that these two spectra are both constituted 

 of fine lines. 



He used ordinary Pliicker tubes having a capillary part 

 in the middle, which are quite suitable for this particular 

 investigation. 



At the commencement, the bands of azote are always 

 seen, even with argon which is supposed to be perfectly 

 pure, but they disappear at the end of a certain time. 



At the pressure of three millimrtres the most brilliant 

 spectrum is obtained, and in this case the light is red. 

 On diminishing the pressure and placing a Leyden jar in 

 (he circuit, the colour of the discharge is seen to pass 



