46 Colouration in Animals and Plants. 



seen. Thus, the young tiger is spotted, and BO is the young lion; 

 but, whereas in the former case the spots change into the well- 

 known stripes (which are really loops), in the latter they die away. 

 The horse, as Darwin long ago showed, was probably descended 

 from a striped animal, as shown by the bars on a foal's leg. But 

 before this the animal must have been spotted ; and the dappled 

 horses are an example of this ; and, moreover, almost every horse 

 shows a tendency to spottiness, especially on the haunches. In the 

 museum at Leiden a fine series of the Java pig (Sus vittatus) is 

 preserved. Very young animals are banded, but have spots over 

 the shoulders and thighs ; these run into stripes as the animal grows 

 older; then the stripes expand, and, at last meeting, the mature 

 animal is a uniform dark brown. Enough has now, I trust, been 

 said upon this point to show that from spots have been developed 

 the other markings with which we are familiar in the animal 

 kingdom. 



The vegetable kingdom illustrates this fact almost as well. 

 Thus, the beautiful leaves of the Crotons are at first green, with few 

 or no coloured spots ; the spots then grow more in number, coalesce, 

 form irregular bands, further develop, and finally cover the whole, 

 or almost the whole, of the leaf with a glow of rich colour. Some 

 of the pretty spring-flowering orchid callitriche have sulphur-yellow 

 petals, with dark rich sepia spots ; these often develop to such an 

 extent as to overspread nearly all the original yellow. Many other 

 examples might be given. 



Hitherto we have started with a spot, and traced its develop- 

 ment. But a spot is itself a developed thing, inasmuch as it is an 

 aggregation of similarly coloured cells. How they come about may, 

 perhaps, be partly seen by the following considerations. Definite 

 colour-pattern has a definite function that of being seen. We may, 

 therefore, infer that the more definite colour is of newer origin than 

 the less definite. Hence, when we find the two sexes differently 

 coloured, we may generally assume that the more homely tinted 

 form is the more ancient. For example, some butterflies, like the 

 gorgeous Purple Emperor (Apatura iris), have very sombre mates; 

 and it seems fair to assume that the emperor's robes have been 

 donned since his consort's dress was originally fashioned. 



That the object of brilliant colour is display is shown partly by 

 the fact that in those parts of the wings of butterflies which overlap 

 the brilliant colour is missing, and partly by the generally brighter 



