34 Lacertidx. 



in L. agilis, which has a short and thick tail, individuals with the organ 

 in a regenerated condition appear to me as frequent as in most other 

 species of the genus, and certainly more than in L. echinata, which has 

 the longest and most whip-like tail. 



10. According to Eimer, * whose views have been endorsed by Cope t 

 and by Gadow, X but which have been opposed by Mehely,§ the primi- 

 tive type of Lizard is striated, the original light and dark streaks 

 breaking up into spots, and these spots, further becoming confluent 

 into transverse lines, tend to form cross-bands, whilst, in another 

 direction, the markings disappear altogether ; in the course of the 

 changes — ontogenetic or phylogenetic, as the case may be — the pattern 

 on the posterior part of the body anticipates the evolution of that on 

 the anterior part. 



In most cases the young show a more primitive pattern than the 

 adult, only very exceptionally the reverse (see under Eremias luguhris). 

 The more advanced pattern, on the other hand, may appear at birth, 

 and forms in which this is the case are therefore to be regarded as the 

 most remote from the primitive type. 



The ancestral type of Lacerta I conceive to have had five white 

 streaks, separated by black, on the upper surface, and three, also 

 separated by black, on each side — 11 white streaks in all. Of these, 

 the outer dorsal starts from the supei-ciliary border and is prolonged 

 on the tail ; the upper lateral starts from the posterior corner of the 

 eye, passes above the tympanum, and ends above the hind limb ; the 

 median lateral originates on the upper lip, passes through the tym- 

 panum, above the fore limb, ends on the anterior side of the thigh, 

 reappears on the posterior side of the thigh, and is continued on the 

 tail ; the lower lateral proceeds from the lower lip, extends on the 

 anterior side of the fore limb, and reappears on each side of the belly, 

 ending on the lower anterior side of the thigh. This arrangement is 

 exemplified by the young L. agilis, var. exigua, assuming the pale 

 brown colour between the black edges of the white dorsal streaks to 

 have been originally white also, i| but it is likewise to be traced, though 

 in a less primitive condition, in some young of the typical form of that 

 species. I regard tbe disposition of the streaks in the young Acantho- 



* Arch. f. Naturg. ]881, p. 239, pis. xiii-xv. 



t Bep. U.S. Nat. Mus. f. 1898, p. 569, pi. v (1900). 



X Proc. E. Soo. Ixxii, 1903, p. 109, pis. iii-v, and Proc. Zool. Soc. 1906, i, p. 277, 

 tigs. 



§ Ann. Mus. Hung, v, 1907, pp. 80 & 477. 



II The ideal primary striation, as seen on the nape of some Nucras and Acantho- 

 dactyhis, has not actually been observed in L. agilis, but I expect it will be found 

 some day, when larger series of young of the var. exigua can be examined. 



