TELEGOl'JY AND REVERSION. 125 



how are tliey to be accounted for? The only other feas- 

 ible explanation that occurs to me is, that in the numerous 

 stripes across the sides, and in the spots over the hind 

 quarters of Romulus, we have an instance of an abrupt 

 form of variation. On this assumption, the resemblance 

 of Romulus in his markings to a Somaliland zebra must 

 be considered a mere coincidence. 



The evolution of stripes in the Equidge doubtless occupied 

 many centuries. Stripes imply at the outset a concentra- 

 tion of pigment in certain definite areas, and later the 

 disposition of the pigment to form hardly appreciable ill- 

 defined bauds, or it may be to first form irregularly arranged 

 spots, which afterwards unite to form wavy bands, the 

 edges of which are later smoothed. But stripes in the 

 zebras also imply a lightening of the intermediate spaces 

 and other intricate and complex changes. By examining 

 the hair of Romulus one seems to get a hint of how the 

 striping has been brought about. The hairs making up 

 many of the dark bands are at their inner ends of the same 

 or almost the same colour as the inner ends of the hairs 

 in the light intermediate spaces. At present (October) the 

 hairs in the region of the shoulder are quite two inches in 

 length. If some hairs are taken from the shoulder stripe 

 and others from one of the light-coloured spaces near the 

 shoulder-stripe, the inner ends of both samples are seen to 

 be of a yellowish-grey or ash colour. But while the inner 

 ends agree, the outer two thirds or so distinctly differ. 

 The hairs from the dark stripes for quite two thirds of 

 their length are dark brown or almost black, while the 

 hairs from the light space are for quite two thirds of their 

 length of a pale ash colour, while the remaining third — 

 the outer or distal part — is of a light brown colour.^ It is 

 doubtless possible that the result of crossing extreme forms 

 may be the formation of new and unheard of varieties — 

 may, in fact, lead to progressive changes ; but for reasons 

 to be given later I consider that this but seldom occurs, 

 that in fact the intercrossing of extreme forms must almost 

 * Tlie difference in the colour of the hairs is more pronounced in summer. 



