ioo NATURAL SCIENCE. Feb., 1896. 



change in colour of the larvae themselves from green to brown, and 

 is perhaps connected with a similar change of colour in solutions of 

 chlorophyll when exposed to the action of organic acids or bright 

 sunlight. 



There seems little reason to doubt that Mr. Poulton's conclusion 

 as to the green colouring matter in this case is quite correct, and 

 that we have here a genuine example of the transference of pigment 

 from one organism to another, with relatively slight change. As to 

 the direct bearing on the physiology of the caterpillar, we have no 

 detailed evidence ; perhaps the following may not be thought to 

 transgress the bounds of legitimate speculation. It is a well-known 

 physiological fact that if one mammal be fed to excess with the fat of 

 another, the fat which is ultimately deposited in the tissues of the 

 former does not exhibit the specific peculiarities of the normal fat of 

 the animal, but partakes more or less of the characters of the fat of 

 the food. In other words, an animal is unable to impress its own 

 individuality on the fat of its food, if this be ingested in very large 

 quantity. Now both chlorophyll and etiolin undoubtedly contain a 

 basis of lipochrome pigment, and the lipochromes are very frequently 

 found associated with fats ; in the case of chlorophyll, indeed, the 

 association has been directly affirmed. Is it not possible that in the 

 caterpillar — a notably voracious feeder — a process occurs similar to 

 that noted above for mammals ? That is, may not caterpillars, which 

 have a practically unlimited food- supply, be unable to assimilate 

 completely all the fat ingested, but yet have the power of storing-up 

 in their tissues this extra fat, and with it the pigment with which it 

 is associated in the food ? If this be so, we can understand why in 

 Mr. Poulton's experiments, when larvae of set 2 were removed and 

 furnished with etiolated leaves, they failed to develop green pigment, 

 even when they continued to live for about a fortnight under the new 

 conditions. These larvae had previously been starved, and so were 

 perhaps unable completely to assimilate all the constituents of the food 

 finally supplied. According to this theory, food containing chlorophyll 

 is a richer diet than food without it, and leads to the deposition of 

 extra reserves in the tissues, and indirectly to additional pigmentation. 

 The theory is not inconsistent with the fact observed by Mr. Poulton, 

 that in some species (Smerinthus ocellatus, for example) the green 

 colouring-matter may be found also in the eggs, and so be passed on to 

 a second generation. As nutrition in the butterfly is unimportant, 

 there is reason to believe that the caterpillar must provide the 

 nutritive substance subsequently employed in the formation of yolk, 

 and the association of lipochrome pigment with yolk is frequent 

 enough ; possibly the reserve substances deposited in the tissues may 

 in such cases be directly employed in the production of yolk. 



(The References will be given at the end of Part II.) 



Marion J. Newbigin. 



