162 THE GENESIS OF SPECIES. [CHAP. 



than the unions indicated between India and Australia, 

 China and Australia, China and North America, and India 

 and Africa. 



Pleurodont lizards are such as have the teeth attached 

 by their sides to the inner surface of the jaw, in contradis- 

 tinction to acrodont lizards, which have the bases of their 

 teeth anchylosed to the summit of the margin of the jaw. 



INNER SIDE OF LOWER JAW OF PLETJRODONT LIZARD. 



(Showing the teeth attached to the inner surface of its side.) 



Now pleurodont iguanian lizards abound in the South 

 American region ; but nowhere else, and are not as yet 

 known to inhabit any part of the present Continent of Africa. 

 Yet pleurodont lizards, strange to say, are found in Mada- 

 gascar. This is the more remarkable, inasmuch as we have 

 no evidence yet of the existence in Madagascar of fresh- 

 water fishes common to Africa and South America. 



Again, that remarkable island Madagascar is the home 

 of very singular and special insectivorous beasts of the 

 genera Centetes, Ericulus, and Echinops; while the only 

 other member of the group to which they belong is Solen- 

 odon, which is a resident in the West Indian Islands, Cuba, 

 and Hayti. The connection, however, between the West 

 Indies and Madagascar must surely have been at a time 

 when the great lemurine group was absent ; for it is diffi- 

 cult to understand the spread of such a form as Solenodon, 

 and at the same time the non-extension of the active le- 

 murs, or their utter extirpation, in such a congenial locality 

 as the West Indian Archipelago. 



