4 
LECT^RE^VH. 
subdivisions, and .exliibit the artery and vein in 
a more_ simple state of ramification than in the 
Frogs.^ In the Serpent tribe the structure of the 
lungs seems to run between that of Frogs and 
Lizards ; the upper part being divided internally 
into smaller cells, while the remainder degenerates 
into a mere continued bladder as in the Lizards. 
The whole tribe of the proper or Linnaean 
Amphibia, viz. the Tortoises, Frogs, Lizards, and 
Serpents, possess a kind of voluntary power by 
wLich they are able at pleasure to suspend their 
respiration ; so as to continue for a long timo 
without breathing, by retaining air within their 
lungs, instead of being obliged to discharge it 
frequently, as quadrupeds and birds are obliged to 
do. LinnjEus therefore, among other characters 
of the Amphibia gives that of arbitrary lungs, 
pulmones arbitrarii, or such as can at pleasure 
suspend respiration, without injuring the animal. 
Upon this principle it is that these animals may 
be confined in the closest situations without seem- 
ing to suffer any material inconvenience, and 
many of them are calculated for residing with al- 
most equal ease either on land or under Tvater. 
In Frogs so strong is this^power of retahiing air 
