DE(JEXEKATIOX IX LIMBS OF LIZAIIDS. 2/0 



changes in its near all^". Similarly with the monodactylous con- 

 dition of the hind-limb and the complete absence of the fore-limb 

 exhibited by G. viacrolcpis. Slightly different mutative changes 

 in the different individuals of the same species, along with later 

 germinal intermingling within the species, may thus have pro- 

 duced all the variety we now find, a variety which almost suffices 

 to give the appearance of a continuous series between the two 

 extremes. 



We have no evidence to show^ that the germinal changes 

 which have already brought about limb degeneration in 

 Chcmiaesaura will be continued, and that C. aenea will pass into 

 the stage represented by C. anguina, and the latter into that of C. 

 inacrolepis, and that ultimately the limbs of all three species will 

 disappear, as has already happened to the fore-limbs of the last- 

 mentioned. There is much in favour of the belief that degenera- 

 tive stages, as we know them, are permanent for the time being, 

 and are not necessarily stages in the direction of still further 

 losses. Thus, we have palaeontological evidence that the tarso- 

 metatarsus of the ostrich, comprising the large middle metatarsus 

 and the incomplete second and reduced fourth metatarsi, has 

 vmdergone no further change since the Pliocene days of the 

 Siw-alik deposits, nor that the large third toe and the fourth small 

 one have varied in their relative size during this long period. The 

 vestiges of the hind-limbs and girdles in boas and pythons can, 

 with no justificacion, be held to be still undergoing changes which 

 will ultimately complete their degeneration ; similarly wdth the 

 relics of the hind-limbs or their girdles in Cetaceans and Sirenians. 

 In the course of evolution factorial changes have brought the 

 structures to the condition in which we now find them ; but we 

 have no reason to suppose that further changes will occur in the 

 same direction, and thus complete the degeneration already 

 initiated. 



