XV1 INTRODUCTION. 
The first of the orders, the Testudinata, includes the 
Tortoises and Turtles. Although we have no species 
of this order inhabiting the British islands, yet as there 
have been occasionally stray individuals of the marine 
forms brought to our coasts, and even taken alive, and 
as many species of the land and fresh-water forms are 
often kept living in our gardens and ponds, it may not be 
uninteresting or inappropriate to offer a short account of 
their general organization and habits. Their structure, as 
has been already observed, differs in a very remarkable 
manner from that of the rest of the class. The arrange- 
ment of the osseous system has already been glanced at ; 
and it offers the most remarkable tendency to consolida- 
tion and strength, to the sacrifice of facility and variety of 
motion. In the terrestrial forms especially this character 
is carried to an extreme degree; the vertebra, the ribs, 
and the sternum are all closely and inseparably united 
into a compact solid case, in which the whole of the 
viscera, and, during rest, the head, limbs, and tail are 
covered and protected. So strong is this shell, both from 
the thickness and solidity of its parietes, and from the 
arched form of the superior portion, that in many species 
it will bear immense pressure without injury. In certain 
genera, however, this bony box, although still exceedingly 
strong, has certain parts which are rendered moveable, for 
the still more complete protection of the enclosed organs. 
Thus in the genus Kinixys, a terrestrial form, the lumbar 
portion of the carapace, or upper part of the case, is 
moveable, so that the animal has the power, when the 
limbs and tail are withdrawn within it, to close that move- 
able piece against the posterior part of the sternum; and 
in the genus Pyzis the anterior portion of the sternum 
exhibits this peculiarity in a still more remarkable degree. 
