7 o 



BIOLOGICAL LECTURES. 



We may commence with Tropidurus. More than 400 speci- 

 mens of this lizard were collected. It was found on Inde- 

 fatigable, James, Jervis, Duncan, Charles, Barrington, Hood, 

 Gardner, Chatham, Bindloe, and Abingdon. On Charles it 

 was exceedingly rare and on Tower no specimen at all was 

 discovered ; on Tower it has probably been extinguished by 

 the sea-birds, which are found there in enormous numbers. 



Each island possessed only a single species of Tropidurus, 

 all the individuals of one island belonged to one species; and 

 nearly every island had its peculiar species or race. 



I have counted the number of the scales round the middle of 

 the body in all the specimens and found the following results : 



The total variation for all forms is 53-101, not less than 48; 

 but in none of the single islands is the variation in the number 

 of scales more than ten. The number ten we find on Inde- 

 fatigable, Albemarle, Chatham, Charles, Abingdon ; the number 

 eight on Barrington, Hood ; the number six on James, Jervis, 

 Bindloe, Gardner, Duncan. I do not doubt that in different 

 forms, after an examination of a larger number of specimens, 

 the extension of the variation will be found wider ; but prob- 

 ably it will rarely be more than ten. It is interesting to notice 

 that on the larger islands the variation is greater than in the 

 smaller ones. 



