Page:Mind (Old Series) Volume 9.djvu/431

 THE REGENERATION OF LOST PARTS IN ANIMALS. 419 so-called ' blue lizard ' of Capri, Lacerta LUfordi, has normally a large amount of pigment present in its epidermis, to which it owes its dai-k colour, and in this species a regenerate tail acquires and retains permanently a darker tint than the rest of the body. Now Fraisse suggests (in direct antagonism to Ehner's view) that this darkening of the regenerate member is a case of reversion, and that the presence of epidermal pigment is au ancestral character. He supposes that the gradual imitative adaptation of colour to habitat was gradually obtained by the advance (or return) of the black chromatophores from the epidermis into the cutis. We have thus traced in the phenomena of regenerative growth, a tendency to the attainment of the required end by a repetition of embryonic processes ; and also a marked tendency to the re- capitulation of phylogenetic history. To return to Mr. Haldane. Proceeding on a philosophical doctrine of the relation of the categories of mechanism and teleology, he argues against the current physiological assump- tions regarding the nature of life, which take it to be explicable or at least conceivable as a manifestation of mechanism or an effect of definite physical causes. And he makes use of the phenomena of regeneration of lost parts in contending that we must sublate our view of the nature of life from a mechanical or cause-and-effect category to a category of reciprocity, and from that further to one in which the parts must be regarded as deter- mined in relation to an idea of the whole ; in other words that organic processes cannot be reduced to series of causes and effects, or to what is the same thing, matter acting as a vehicle of energy. If a newt's limb be amputated, whether the line of amputation be transverse, oblique, or irregular, and at whatever point it be taken, the cells concerned in the process of regenera- tion succeed in accurately reproducing the limb. They do not do their work blindly, but, allowing for new and inconstant cir- cumstances, adjust their behaviour to the exigencies of the case. In this phenomenon, Mr. Haldane sees a certain 'purposiveness,' a relation to ultimate function, which cannot be due to the action of mere neuro-muscular or intra-cellular mechanisms. And unless we are to assert the existence within the organism of phenomena altogether different from those outside it, we must acknowledge a force connecting generally the organism and its surroundings, to which is subordinated the force governing the motions of the animal. On this phenomenon of the regeneration of a newt's limb, and on certain apparent evidences of elective volition in the earth- worm, Mr. Haldane builds his argument, and he builds it strongly and carefully. But I think that the facts stated in this paper have a very important bearing on philosophical speculations such as his. For we have seen that histologically the renewal of a