Lacerta. 33 



7. The rather large, rhombic or hexagonal, keeled dorsal scales of 

 L. agilis lead through various gradations to the smooth granules of 

 L. ocellata and of many of the members of the L. muralis group ; a 

 tendency to imbrication, more or less marked in some specimens of 

 L. viridis, leads to L. 'princepg and, with an increase in size, to 

 Algiroides and Psammodromus. The distinctly overlapping character 

 of the large plates on the lower parts in L. agilis is lost in the 

 L. muralis group, and the number, 6 or 8, of longitudinal rows of these 

 plates, gradually merging into the lateral scales, may be increased, 

 as in L. ocellata and galloti, or the differentiation may be more 

 abrupt through disintegration of the small outer plates, as in many 

 members of the L. muralis group. The large plates forming the 

 so-called collar may be reduced in size and increased in number, at the 

 same time losing the notches between them on their free border, 

 as in L. muralis and allies ; or they may become adherent to the 

 middle of the breast, as in Aeanthodactylus ; or the whole collar may 

 lose its freedom, and the gular scales pass gradually into the ventral 

 plates, as in Psammodrcmius. 



8. Of all the species of Lacerta, L. agilis has the shortest digits, and 

 they are not at all compressed. In the L. muralis group the digits 

 become longer and more compressed, especially distally, as the climbing 

 habits»become more and more marked. The series L. taurica-campes- 

 tris-serpa is instructive in this respect. In L. agilis the subdigital 

 lamellae are smooth and undivided, or divided into two. In Lizards 

 adapted for arid sandy tracts the subdigital lamellae acquire one or 

 several keels (Latastia, Aeanthodactylus, Eremias), and a series of 

 pointed scales may form a serration or fringe on one or both sides of 

 the digit (Aeanthodactylus). These are clearly adaptations to a special 

 mode of life. I cannot conceive the direction of the series reversed, 

 viz., compressed or serrated digits leading to the simple form of 

 L. agilis. 



9. If ontogeny is a guide to phylogeny, L. agilis, which has the 

 shortest tail in the genus Lacerta, must be regarded as the most primi- 

 tive species in this respect. Lizards at birth having invariably a shorter 

 tail in proportion to the body.* Mehely, who considers the longer tail 

 as the more primitive, observes that extremely long, slender, whip-like 

 tails — as in L. oxycephala, for instance — are endowed with greater 

 fragility. This may be true — and here again I would look upon 

 extreme fragility of the organ as a specialization, but I must say that 



* Measurements of head and body and tail in specimens at birth of, four 

 species : — L. agilis, 26 + 29 mm. ; L. viridis, 27 + 27 mm. ; L. vivipara, 20 + 

 22 mm. ; L. muralis, 22 + 28 mm. 



