322 DR. H. GADOW ON EVOLUTION [Mar. 20, 



with tiny scales, and as a rule these are sharply marked ofi' against 

 the much larger ventrals. 



Femoral j}ores. — The commonest numbers are 20 and 21, the 

 usual range extending from 19 to 23. Quite excej)tional was the 

 occurrence of 17/20 in a tall specimen from Ayutla, and another 

 from the foot of Los Cajones. 18 did not occur. 23 pores, 

 mostly on one side only, were observed 4 times. 



Length of hind limb. — The claw of the fourth toe usually 

 readies the ear, but in one specimen from Ayutla it only reaches 

 the arm, whilst in another fi'om exactly the same locality the 

 limb is so long that the claw extends to the eye. 



Coloration of under 'parts. — The collar is noi-mally black in both 

 sexes. Even in the young of only 50 or 56 mm. in length, it . 

 begins to become dusky or sj)eckled on the sides. Sometimes, 

 however, even in adult males during the breeding-season, the 

 collar is not black but leaden, in rare cases ahnost dull whitish. 

 In other cases the black spreads sometimes onto the neighbouring- 

 parts of the throat ; in a specimen from Los Cajones the whole 

 throat is blue-black, and in all the four specimens from San 

 Domingo, Lsthmus, the throat is black. In the majority of cases 

 the throat is whitish or pale lead-colour. Lastly, in the adult males, 

 and even in some females of the specimens which I observed and 

 caught at Agua fria, the throat was light brick-red, but this red 

 fades away completely in spirit-specimens. 



Chest and helly are whitish or greenish yellow ; in the males 

 more or less suffused with dark blue, chequered towards the sides 

 and on the ventral surface of the thighs. But this blue, rarely 

 verging towards black, is only suffused and is restricted to the 

 deeper, cutaneous strata of the scales. The under surface of the 

 tail is white, bordered or chequered Avith blue on the sides. 



The colour-jyattern of the hack (text-figs. 74, 75, and 81 E) 

 consists of an almost black to dark olive-grey to ashy-brown 

 ground, broken by 6 to 9 longitudinal rows of white, slightly 

 greenish or yellowish colour. These rows are either entii-e stripes, 

 or one or all of them may be broken up into coherent beads, or 

 into separate spots. This breaking up of the strijjes into spots 

 proceeds upon a definite plan. 



First, the breaking-up increases with the size or age of the 

 lizard, but this does not exclude the existence of old and large 

 specimens which retain their stripes throughout life. 



Secondly, the breaking-up, or the frequency of beads or spots, 

 proceeds from the central stripe or pair of stripes towards the 

 flanks. In this way then in the 7- or 9-striped specimens the 

 central stripe, number 4 or 5 respectively, is the first to break up. 

 In fact, there are none with 9 complete stripes, and there aie but 

 few with 7 complete stripes. Specimens with 8 complete stripes 

 (the stripes 4-4 running parallel, or being joined into an unpaired 

 one on the neck) are not uncommon, but more frequently they 

 are dissolved into many white and bright spots. Then follows 

 pair 3-3, then pair 2-2, which is often represented by a series of 



