March 1, 1893. J 



KNOWLEDGE 



41 



^^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED I 



LONDON: MARCH 1, 1893. 



CONTENTS. 



Caterpillars— Y. By E. A. Butlbe 



Deep Sea Deposits.— First Paper. By llif Eev. II. X 



Hutchinson, B.A., F.G.S 



On certain Low-Lying Meteors. — I. V,\ Oh.\rle! 



ToMLissoN, F.R.S., F.C.S., &c 



Letters :— Uaeold M. Collison ; Dr. A. Brester, Jz. 



W. H. S. MoxcK 



The 7, Argus Region of the Milky Way. By A C 



Rantard.., 



Notices of Books 



Science Notes 



The Constitution of Gases. By J. J. Stewart ... 

 Living Fossils. By R. Ltdekkeb, B.A.Cantab. 



The Face of the Sky for March. By Herbert Sadler 



F.R.A.S ' 



Chess Column. By C. D. Locock, B.A.Oxon. 



PAGE 

 41 



43 



46 



48 



50 

 51 

 51 

 53 



59 



CATERPILLARS.-V. 



By E. A. Butler. 



{Continued from paije 35.) 



THAT the colours of caterpillars have some sort of 

 relation to their surroundings is a conclusion at 

 which one would be able to arrive after even a 

 limited experience in the woods and fields. Thus 

 it would soon be discovered that those larvae that 

 feed in the stems of plants or the trunks of ti-ees, or in 

 roots, or between the skins of leaves, are mostly pale 

 whitish or yellowish, and that those that dwell in the 

 seclusion of a coiled-up leaf are chiefly of a dirty greenish 

 or yellowish white without distinct markings. On the 

 other hand, it would be found that those that feed iu the 

 open are much less uniform in tint, and are often brightly 

 variegated, or at least decidedly coloured, and marked not 

 unfrequently with distinct and intricate patterns of ex- 

 quisite hues, in sharpest contrast with one another — 

 patterns, indeed, which might often be worth the attention 

 of students in a school of art, for the suggestion and 

 elaboration of artistic designs. Moreover, speaking again 

 only of those caterpillars that feed exposed, one of the 

 earliest generalizations the practical naturalist feels him- 

 self in a position to make is, that the two colours to which, 

 out of all the variety of Nature's extensive repertoire, the 

 preference has been given in the vegetable world, viz.. 



green and brown, are also those that prevail in the cater- 

 pillar world, while some others, such as blue, for example, 

 are very rarely to be met with. And, as such caterpillars 

 spend their life amongst vegetation, some on the leaves, 

 others in closer proximity to the stems and branches, it is 

 not unreasonable to conclude that the prevalence of green 

 and brown in their skins is due in some measure to the 

 state of affairs found in the vegetable world ; for the 

 assimilation of the insect to the aspect of its surroundings 

 would render it less conspicuous, and would probably, 

 therefore, to some extent protect it from foes which might 

 otherwise jeopardize its existence. 



But after all, such a conclusion only pushes the enquiry 

 a stage farther back, for, if we accept it, we then need to 

 enquire why these two particular colours are also the 

 dominant ones in the vegetable world ; it cannot here be a 

 case of the imitation of environment, but some other and 

 perhaps more obscure reason would seem to underlie the 

 fact. And here, whatever may have been the case before, 

 we get most distinctly into the regions of chemistry and 

 physiology, for the green colour of plants is due to the 

 presence in their tissues of a particular substance called 

 chlorophyll, and the presence of this is again due to 

 physiological changes in the plant brought about through 

 the influence of the sun's rays, so that again the enquiry 

 would be pushed back a stage, for we should need to ask 

 why chlorophyll is green. While, therefore, it will be a 

 distinct advance in knowledge if it can be shown that the 

 colours of certain living baings are to any extent deter- 

 mined by those of the inanimate objects around them, we 

 must not lose sight of the fact that this is by no means 

 the end of the matter, that we have advanced but one step 

 along the path of truth, and that many more may be 

 necessary before it is possible to establish in all their 

 completeness the connections that exist between the 

 forces of Nature and the present conditions of the various 

 animate and inanimate organic bodies we see around us. 



Bearing these cautions in mind, then, we may proceed 

 to consider in a little more detailed way, some of the chief 

 facts connected with the colours and markings of cater- 

 pillars. If the colours of caterpillars are affected by their 

 surroundings, it would appear that the result would be 

 produced in one or other of two ways, either by the colour 

 of the food itself affecting that of the tissues of the body 

 and the blood, and this colour then appearing through the 

 transparent skin, or, on the other hand, by the presence of 

 some sensitiveness in the indi\idual, which enables it 

 unconsciously to respond to the nature of the light falling 

 upon it from surrounding objects, and produce pigments of 

 one colour under the influence of light of one kind, and of 

 another colour with a preponderance of light of a different 

 kind. Caterpillars feeding upon green leaves, and having 

 thin transparent skins, might thus, on the first hypothesis, 

 be expected to show a tendency towards a green colour, and 

 this has been proved in some cases to account for the 

 greenness of larvfe. Indeed, when such larvte are not green, 

 it IS not necessarily through the absence of that colour in 

 their tissues, but often merely because it is concealed by 

 other pigments deposited in the skin. These facts have 

 been established by Mr. Poulton, by means of a series of 

 very elaborate experiments, which lead also to the second 

 hypothesis mentioned above. 



To determine this latter point, namely, the influence 

 which the surroundings exercise by their mere presence, he 

 experimented with several kinds of larvfe, but especially 

 with those of the pepper moth {Amphidnsis hetularia), as this 

 proved to be by far the most susceptible to external 

 influences, and therefore the best for experimentation. The 

 food uniformly supplied being the leaves of the black 



