f>2 
SYSTEM OF NATURE. 
nently condemning the entire work as too imaginative, 
when the following extract from a letter from Professor 
Owen suddenly arrested my attention. u I lose no time in 
replying to your very welcome letter, because I have a 
statement to make which justifies your disinclination to 
regard the Reptilia of Cuvier as including two distinct 
classes. Not any of the Batrachia have a single auricle; 
for though the venous division of the heart has a simple 
exterior , it is in reality divided internally into two sepa¬ 
rate auricles , receiving respectively, the one , the carbonized 
blood of the general system; the other and smaller , the 
aerated or vital blood from the lungs. This I have found 
to be the case successively in the frog and toad , the salaman¬ 
der and newt , and lastly , in the lowest of the true Am¬ 
phibia , the Siren lacertina , fyc. n * This taught me an 
important lesson; — to receive all statements, even from 
the very highest source, with some degree of hesitation. 
I recollect no assertion, in the entire range of comparative 
anatomy, that has been received with such implicit faith 
as this dictum of Cuvier, on the difference in the structure 
of the heart in these two groups, yet none could have met 
with a more flat and decided contradiction. Being thus 
compelled to renounce the circulation as affording a suffi¬ 
cient ground for dividing the reptiles, and being equally 
unwilling to abandon a division which so exactly sub¬ 
served my own idea of natural arrangement, it occurred to 
me that the metamorphotic form, and more particularly 
metamorphotic respiration, might form the groundwork of 
a perfectly natural division ; but I soon found that liana 
and Salamandra alone possessed these characters, while in 
* Kirby’s Bridgw. Treat, ii. 413. See also Zool. Trans, i. 213. 
