272 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Nov., 1904. 



what appear to be instances of primitive coloration 

 are really cases of adaptation to environment indepen- 

 dently acquired. 



That the dominant type of coloration among; primi- 

 tive animals took the form of longitudinal stripes 

 seems to be a very wide-spread belief. These stripes 

 are next supposed to have given way to spots, and 

 these latter either became re-arranged to form trans- 

 verse stripes, or mottling-s, or disappeared altogether, 

 leaving a perfectly uniform coloration unrelieved by 

 any markings, or at least any very conspicuous mark- 

 ings such as form a pattern. This orderly sequence 

 seems to imply that these patterns have followed a 

 preordained line of evolution; and that whatever the 

 cause of their origin may have been, the later phases 

 arising therefrom develop independently of the en- 

 vironment. This is by no means a generally accepted 

 view. 



Eimer supposes " that the fact of the original pre- 

 valence of longitudinal striping might be connected with 

 the original predominance of the monocotyledonous 

 plants, whose linear organs and linear shadows would 

 ha\e corresponded with the linear stripes of the 

 animals; and further that the conversion of the striping 

 into a spot-marking might be connected with the de- 

 \elopment of a vegetation which cast spotted 

 shadows. It is a fact that several indications exist 

 that in earlier periods the animal kingdom contained 

 manv more striped forms than is the case to-day." 

 " This supposition," he goes on to say, " is also sup- 

 ported somewhat by the fact ' that at present strongly 

 spotted forms mostly occur in places with spotted 

 shadows, the longitudinally striped more in grassy 

 regions. . . . Cross-marking is perhaps to be 

 connected with the shadows, for example, of the 

 branches of woody plants — thus the marking of the 

 wild cat escapes notice among the branches of trees.' 



That these several types of markings are, in many 

 cases, direct survi\'als enjoying a transient existence, 

 like many other vestigial characters, is highly prob- 

 able, Init in others thev, with almost equal certainty, 

 represent comparatively recent developments. 



Thus the spots in the young lion and the faint traces 

 thereof in the adult female are almost certainly 

 remnants of an earlier and more emphatically spotted 

 phase common to the adults of both sexes. But it is 

 surely possible that in many cases these markings may 

 be remnants of an earlier spotted immature stage when 

 the young derived benefit from the protection these 

 markings afforded. In such cases the adults may 

 have been quite differently coloured ? 



The possibilitv that the coloration may, in the 

 ancestral forms, ha\e been of one type for the adult 

 and another for the immature stages, and that the 

 ancestral immiiture stages may be reproduced at the 

 corresponding period of development to-dav, is one 

 that seems not to h;i\e received fair consideration. 

 Evidence in l,i\our of this view- will be submitted 

 presently. 



According to the prevailing opinion, we have some- 

 thing like a recapitulation of past types of coloration, 

 the markings of ancestral adult stages being repro- 

 duced in the immature stages of to-day. On this as- 

 sumption we must suppose either that this immature 

 coloration is now of no protective value, or that the 

 descend.ints of these spotted or striped forms, .as the 

 case may be, require the ancestral adult protective 

 colours only duiing the period of immaturity ; or that 

 this coloration belongs to the class of correlated varia- 

 tions and has no significance in a large number of 

 cases. 



But even this view cannot be reconciled with 

 Elmer's intreprctation of the significance of these 

 markings. If longitudinal stripes are the result of 

 adaptations to foliage of monocotyledonous plants, 

 and spot marking to an adaptation to foliage of vegeta- 

 tion which cast spotted shadows, then the longitu- 

 dinal markings of many animals of to-day must be 

 quite out of harmony with their environment, and their 

 survival shows that in these cases at least the corre- 

 spondence between the markings and the type of 

 foliage need not be a very close one, since the longi- 

 tudinal stripes developed to harmonize with linear 

 foliage serves ecjually well amid foliage which casts 

 spotted shadows. 



Transverse stripes, at least, it must be admitted, owe 

 their origin to adaptation to totally different environ- 

 ments. Originallv de\'eloped for the sake of affording 

 protection amid linear foliage, as in the tiger, for 

 instance, they ha\e almost certainly been acquired 

 Je novo in the case of the zebra, where they serve to 

 protect the animal on account of the absence of foliage 

 of any sort. 



The contention that longitudinal striping was de- 

 veloped in response to linear foliage is lacking in 

 cogency. Vertical stripes would have served the pur- 

 pose better, supposing that the direction of the stripes 

 was a matter of prime importance. The widespread 

 occurrence of longitudinal stripes probably depends on 

 a deeper stimulus. 



The definite and orderly sequence of colour, which 

 many animals exhibit in the course of development, 

 seems to show that in many cases the markings of the 

 immature stages are really reproductions of an 

 ancestral adult livery. This is well seen in cases 

 where the male and female have a distinct livery. Here 

 the females and young are often precisely similar in 

 dress, and bear a remarkably clo.'^e resemblance to the 

 adult stages of both sexes of more primitive but closely 

 allied species. Among birds there are many illustra- 

 tions of this. A large number of animals, however, 

 afford no clue as to whether the colour of the im- 

 m.iture indi\idual is ancestral or newly acquired ; 

 whether it is an ancestral adult or an ancestral juvenile 

 coloration. The larval Alpine Newt, for example, is 

 conspicuously longitudinally striped. Even while still 

 within the egg these markings can be seen. There is 

 a median dorsal black stripe which bifurcates on the 

 head, and a lateral stripe, also black. Later, black 

 pigment cells wander into the transparent ground 

 colour, and eventually the black upper and red under 

 surface of the adult is acquired. The stripes of cater- 

 pillars are not easily accounted for. Are these in- 

 dependently acquired markings, or inherited ancestral 

 larval markings? They certainly can have nothing to 

 do with the adult coloration. 



With the birds the problem becomes still more com- 

 plex, inasmuch as, in the precocious types at least, we 

 may have three separate plumages : (a) the nestling ; 

 (b) of the fully-flcdgcd " immature " stage, which may 

 be the same as that of the female ; and (c) the adult 

 stage, i.e., the plumage worn by the male only, or by 

 both sexes. 



With regard to the " immature " stage it is worthy 

 of comment that, as Prof. Newton has pointed out, 

 " Throughout the class Avis it is observable that the 

 voung, when first fledged, generally assume a spotted 

 plumage of a peculiar character — nearly each of the 

 body-feathers having a light-coloured spot at its tip — 

 and this is particularly to be remarked in many groups 



