30 Lacertidse. 



reduction or division of the lower part of the subocular, ultimately 

 excluding it from the oral border. 



5. Formation of a transparent disc in the lower eyelid, and ultimate 

 fusion of the latter with the upper eyelid. 



6. Formation of a denticulation or a fringe of scales in front of the 

 ear-opening. 



7. Reduction or increase in the size of the scales on the body and 

 tail, decrease in the imbrication of the shields on the belly, reduction 

 and loss of the collar. 



8. Lengthening and compression of the digits, accompanied by an 

 increase in the number of inferior lamellae ; multiplication of the 

 scales round the digits; development of keels on the subdigital 

 lamellse, or of a pectination on one or both sides of the digit. 



9. Lengthening of the tail, perhaps accompanied by an increased 

 fragility of the organ. 



10. Modification of the patterns of markings, starting from stria- 

 tion, leading on the one hand to ocellation (in longitudinal, irregular, 

 or transverse series), on the other to spotting (longitudinal, irregular), 

 reticulation, and barring. Assumption of vivid colours. 



I will now explain how these principles work out when applied to 

 the Lacertidse, and to the species of Lacerta in particular : 



1. Teeth are present on the pterygoids in all members of Sections 

 I and II of the genus Lacerta, forming a cluster of two or three series 

 in L.agilig undparva. In Section IV they persist.'constantly or with rare 

 exceptions, in L. taurica, peloponnesiaca, Irandtii, Isevis, and jayakari, 

 but disappear in the other species, with rare individual exceptions. 

 They are usually absent in the other sections. 



2. The subject has been discussed in relation to Prof. v. Mehely's 

 proposal to reverse the series as I conceive it, and I have appealed, in 

 support of my contention, to examples drawn from other groups of 

 Yertebrates ; my opinion is also based on considerations derived from 

 a study of Eeptilian morphology in series which palaeontology con- 

 clusively shows to have evolved in a definite direction. In the case of 

 Lacerta, the intemarial bony space and the postfronto-squamosal arch 

 are broader in L. agilis than in any other member of the genus.* The 

 osteodermal plates are most i-educed in the forms with strongly 

 flattened skulls ; on the other hand, they increase in development in 

 L. viridis, ocellata, and galloti (in a different line of evolution), in 

 which a flattening of the head and an elongation of the snout obtain 

 as in Section IV, though to a less extent. 



* Gf. Leydig, Die in Deutschlaud lebenden Arten der Saurier, pis. i-iii 

 <1872) ; Degen, P. Z. S. 1910, p. 23, fig. 6. 



