142 THE ZOOLOGIST. 



display the intermediate stage, the adults passing on to the 

 extreme nigriventris. 



The facts of the distribution of this form — it occurs in 

 patches, as it were, on the mainland and islands of Italy, some- 

 times exclusively, sometimes promiscuously — prove that we 

 cannot turn to the all-explaining "external influences" for the 

 cause of this coloration. As the initial tendency is on the part 

 of the male, and an identical development of colour has taken 

 place with the var. rubriventris, where again the throat is the 

 first part of the body to be "ornamented," there is reason to 

 believe that the black here, unornamental as it appears, may be 

 due to sexual selection. To this subject I hope later to refer at 

 more length, and will here merely remark that I am using the 

 term strictly in the sense attached to it by Wallace, as it appears 

 improbable that in different localities the same variety of one 

 species should have been formed through the action of female 

 choice. 



With Anguis fragilis, dark-coloured individuals are occasion- 

 ally met with, and here, in as many cases as have come under 

 my notice,* the black pigment is concentrated on the under 

 surfaces, diminishing towards the throat and tail (only in one 

 instance the tail-end, above and below, was coloured black). 

 The incipient "melanism" proceeds thence up the lateral 

 portions, each scale in its turn receiving a small black central 

 spot, till it reaches the darker zones which usually border the 

 upper parts. Its progress may therefore be quoted as an 

 exemplification of the " infero-superior " development, mentioned 

 by Prof. Eimer in another work. Another process of colour- 

 development, the " postero-anterior," is illustrated in the case of 

 the melanic Einged Snake, Tropidonotus natrix, var. minax, 

 Bonap., where the black colour advances equally along both 

 surfaces, "supra et subtus ater, concolor," as it is described. 

 In the " carbonarius" variety of Zamenis viridiflavus, it is 

 developed on the upper parts only : " supra ater, concolor, 



subtus griseus " In the last-mentioned cases the dark 



colour does not, as with L. Lilfordi, diminish its intensity under 

 the influence of alcohol, a fact which may be of importance as 



I <>r with many reptiles two or more distinct melanotic varieties have 

 been described. 



