1032 LIFE : OUTLINES OF GENERAL BIOLOGY 



It does not seem far-fetched to say that these two opposite 

 trends correspond to our predominantly anaboUc and katabolic 

 alternatives of variation and evolution. But it should be noted that 

 these contrasted characters may to some extent vary independently 

 of one another; thus size, shape, and activity may vary inde- 

 pendently of colouring. We do not as yfet know enough to say that 

 a dominant metabolic ratio must involve the whole organism in its 

 grip, but it cannot be a mere coincidence that the plus variations 

 of lizards include much melanin as well as large size and thick tails 

 (see section on Pigments). What impresses one, however, is the 

 intricacy of the facts and the need of precaution against false 

 simplicity; thus, to take a single instance, the variational tendency 

 in L. serpa pelagoscB is towards a lightening of the ground-colour, 

 yet this is associated with a darkening of the pattern. 



The varied environment on the islands probably acts as a stimulus 

 to variation, but that the different types are due to any simple 

 modification, would be too simple a view, thus while the variety 

 last mentioned tends towards lightening its ground-colour on the 

 island of Pelagosa, a snake characteristic of the same island has 

 varied in the direction of a dark ground-colour, "like roasted coffee- 

 beans". Another complication is that we cannot exclude the possi- 

 bility that some of the apparent trends of variation are the outcome 

 of processes of Natural Selection at present going on, thus there is 

 protective value in lightening of the ground-colour, which tends 

 to inconspicuous green on the mainland and on large islands with 

 dense vegetation. 



In regard to the establishment of variations in colour and pattern, 

 Kammerer has much to say. He distinguishes (A) temporary changes, 

 which are commonly called individual adjustments or transient 

 modifications, from (B) permanent changes, which are more usually 

 interpreted as germinal or constitutional variations. But Kammerer 

 maintains that the permanent changes pass through a phase of 

 fluctuation before they become established. 



The temporary changes (A) may be illustrated by the some- 

 times very pronounced darkening of the same lizard in the course 

 of a day with a high sunshine record, or by seasonal changes 

 in the same individual, which tends to be more brilliant in 

 spring and early summer, more soberly coloured in midsummer 

 and autumn. 



As to fixed colour-changes, Kammerer distinguishes a number of 

 grades, {a) There are progressive individual variations, e.g. when a 

 single lizard becomes permanently ver}^ dark, as if there were a 

 fixation of the modification or adjustment that follows intense 

 sunshine, (h) There are manifold ("plural"!) variations which occur 

 in the majority of the individuals, and seem to be usually occurring 

 progressively in a definite order — first in the adult males, then in 



