156 W. A. KIDD, BSQ.,.M.D.5 B81, M.RIC.S:, FeZcS.) ON 
They resemble birds and lower mammals in the manner of 
reproduction, the young being produced from eggs, but are 
strongly marked off from these two higher classes by the 
absence of hairy appendages to the skin or feathers, though 
certain extinct reptilian forms are believed to have possessed 
feathers. This point touches the much-discussed subject of 
the development of birds from reptiles, which is too large for 
present consideration. Crocodiles show the familiar hard, 
horny appendages to the skin in the form of plates arranged 
close to one another in rows resembling ancient armour, 
which are shown in all the regions most liable to injury, such 
as the back and tail. They are adapted both for life on 
Jand and in the water; but are unable to remain long under 
water. In accordance with their frequent habit of lymg 
near the surface of water they possess a remarkable 
arrangement of the posterior openings of the nasal passages. 
These open as far back as possible in the cavity of the 
mouth just within a short distance of the upper opening of the 
windpipe, and this arrangement allows of the unusual power 
of taking air into the lungs when the anterior portion of the 
cavity of the great mouth is full of water, the external opening 
of the nostrils being placed at the very end of the snout and 
remaining barely visible above water. This constitutes a 
very efficient method of protection from foes and conceal- 
ment from prey. The great rows of teeth and deeply-set 
eyes and small external cars, with their covering for protection, 
need only to be mentioned in the list of the armour, offensive 
and defensive, of the various crocodiles and alligators found 
in the subtropical and tropical regions of the world. 
Tortoises and Turtles possess the well known exoskeleton 
or shell, and this constitutes their first line of defence. Their 
second is that of the horny, toothless beak. Their protective 
structures are almost entirely passive, and the form, texture, 
and arrangement of their carapace or shell is so familiar as 
not to need description here. Suffice it to say that the 
strong, hard substance of the plates, their firm articulation, 
the carefully convex shape of the whole, and the power 
possessed by many of the tortoises of withdrawing their 
head and limbs within the shelter of their movable castle, 
convey a high degree of protection against other than 
human foes. Indeed, one is not surprised at those practical 
old soldiers of Rome having invented or imitated the moving 
fort or testudo, on the lines of this arrangement of the 
protective structure of these reptiles. 
