1903.] and Orthogenetic Variation in Lizards, etc. 117 



disappear, or remain more or less vestigial, varies extremely, and in the 

 adult of both sexes, strictly speaking, the detail of the whole compli- 

 cated pattern is scarcely the same in two individuals from the same 

 locality. 



The midfield, between stripes 3 3, although unimportant, since it 

 never produces any marked characters, undergoes individual changes 

 which remind us of those which occur in other species. As a rule the 

 midfield becomes lighter in the way described above, and it turns 

 green in immature specimens ; later it becomes pale grey-brown, and 

 ultimately more or less mottled and barred with dark pigment. But 

 in one baby of 59 mm. there is a faint, unpaired, central streak, which 

 extends back from the occiput ; and in a specimen of 87 mm. this line 

 is still paler, almost white, bifurcating and extending right down to 

 the rump. These lines represent undoubtedly the 4th pair of stripes, 

 otherwise absent in C. niexicanus. Sometimes, however, pale spots 

 appear in this midfield, arranged in two rows, as indications of the 4th 

 pair of lines. On the other hand, there is in a few cases a distinct 

 narrow, dark line in the centre of the green field. 



The under parts of these lizards are yellowish-white, with a reddish 

 tinge on the under surface of the hind limbs, and on the throat, while 

 the under \ surface of the tail and the whole of its terminal half are 

 often orange to almost brick-red. The collar is never dark. The 

 chest and abdomen of old specimens, especially males, are suffused 

 with greenish or faint blue, while the basal edges of the scales are 

 blackish. After removal of the horny portion of the epidermis the 

 under parts appear quite blue-black, owing to thick pigmentation in 

 the malpighian and in the cutaneous strata. 



Cnemidophorus bocourti, Blgr. (fig. 5, PL 5). 



Structurally, this lizard is but "a slight variety of C. mexicanus, with 

 which it shares the same distribution, except that it is more partial to 

 denser vegetation. It is spotted instead of cross-barred or striped, 

 standing in this respect in the same relation to C. mexicanus as C. striatu* 

 does to C. guttatus. 



All the three stripes are broken up into numerous yellow spots, and 

 a row of equally numerous spots is developed in the fields, and below 

 the original line 1, so that there are in all about 12 to 14 rows of spots 

 across the body. On the lumbar region the spots are more irregular 

 and crowded ; towards the shoulders they become scarcer, and further 

 forwards they disappear altogether, while faint traces of the original 

 pale lines 1 and 2 remain visible. 



In very old specimens the spots are small and irregular, and restricted 

 to the lumbar region, the rest of the back being spotless brown, with a 

 warm reddish tint. 



VOL. LXXII. K 



