80 J. W. SLATER, ESQ., F.C.S., F.E.S., ON 



on a sunshiny day as that of Eristalis itself. May we not rather 

 regard the absence of Eristalis to be consequent on the scarcity or 

 total want in Iceland of the cabbage, on which plant I have captured 

 that tribe in the Faroes, as well as of the thistle, on which blossom 

 I ordinarily take it at home ? 



" The colours of an animal approximate to the colours of the 

 objects by which it is surrounded." P. 66. 



This is most true in respect of all orgauic nature and is corrobo- 

 rated by sundry instances in beasts, birds, reptiles, insects, etc. But 

 when the lecturer proceeds to state " But we rather seek to know 

 how, when, aaul where, and from what materials the colouring- 

 matters are produced, and how they are conveyed to the parts 

 where we find them deposited ? " It is difficult to give a satisfactory 

 answer, various are the hypotheses adduced. The green of many 

 kinds of caterpillar from its similarity to that of the stalk or leaf 

 that holds the insect affords one of the commonest and best known 

 examples of the approximation above mentioned. Some have it 

 that the insect is indebted for its colour owing to its constantly 

 eyeing the verdure by which it is surrounded. (1) But effects 

 produced by eyeing external objects are confined to creatures in a 

 state of parturition. (2) Also all insects in the larva stage are 

 incapable of reproduction. (3) And the green colour is common 

 to both sexes of the larva. Others hold that the green of the 

 caterpillar is occasioned by the creature's absorption of the colour- 

 ing matter through its pores, and others that it is caused by the 

 creature's constantly devouring the "chlorophyll" or colouring 

 matter of the leaf, which forms its habitual food. But these are 

 serious, if not fatal objections to both of these last two theories. 

 In the first place perfect insects (moths for example) as closely 

 resemble surrounding rocks in many cases as catei'pillars do leaves. 

 Now the rocks obviously cannot afford them nutriment, and further, 

 a moth could not possibly imbibe by means of the pores, nor is its 

 proboscis capable of the same work as the jaws of the caterpillar. 

 Also the effect produced by feeding different individuals of the 

 same kind of caterpillar on two different kinds of leaves or on two 

 differently coloured leaves (dark green and light green for example) 

 respectively does not appear to have any result as regards the next 

 generation of caterpillars, while on the other hand a corresponding 

 variation has been noted in the mctlis which are yellowish or white 

 respectively after an indefinite period — say three or four seasons of 

 the larva? being so fed. Then again, leaves such as the larva; feed 

 on, are not the only objects that the larva? resemble. Other larva? 

 of a dark brown tint are quite as undistinguishable from a crooked 

 stick or twig. It is hardly possible to tell the difference between 

 a common oak moth {Tortnx ViHdana) when settled on a tree 

 trunk from a small patch of pale green lichen, or again, another 

 common Tortrix in a similar situation, from bird lime. Probably 

 no one besides myselt has collected the mountain geometra {larentia 



