Systematic Course. 61 
with the spines and ribs of the vertebral column, the 
ventral plates uniting to form a covering for the abdo- 
men, The head, limbs and tail can usually be retracted 
within the dermal armour. The jaws are covered 
with horny epidermis, which takes the place of teeth. 
The group comprises the TYortotses, which have a hard 
shell and ‘feet more or less suitable for walking on shore; 
and the Turtles, which have the shell covered with "soft 
skin and: the feet modified more or less completely for 
swimming. Students should examine the specimens 
in the Museum collection of both turtles and tortoises. 
(2) Crocodilia.—Body partly covered with bony scutes, a long 
‘swimming tail, teeth implanted in sockets, eg., Fish- 
eating gavials with long snouts, carrion-eating muggers, 
with short snouts both represented in the School collection. 
(ce) Lacertilia (Lizards)—Body covered with scales. There are 
generally two pairs of limbs, but one pair and sometimes 
both pairs may be absent. yelids present. Jaws 
firmly united in the middle line. Shoulder-girdle always 
present. Include water-lizards, geckos, cheecha, and 
chameleon. Lizards are chiefly insevtivorous and destroy 
a good many injurious species, especially Acridida. 
The students should compare the scales of the lizard with 
the bony scutes of the crocodile, also the movable eyelid of 
the lizard with the immovable glassy membrane which 
covers the eye of the snake. The Museum contains 
numerous specimens. 
(d) Ophidia (Snakes).—Body covered with scales, generally with 
a series of specially modified scales beneath the body, by 
means of which the snake glides. Fore-limbs and 
shoulder-girdle always absent. Hind limbs occasionally 
present in a rudimentary state (Pythons). Bones of the 
jaws movable on each other. Eyelids transparent and 
permanently closed. Includes all the snakes. 
CLASSIFICATION OF SNAKES.! 
The most important families of snakes are the Boide (Pythons) 
the Colubride (Colubiine snakes), and the Viperide (Viperine snakes), 
(a) Botde (Pythons or rock-snakes).—These snakes are often of 
immerse size. They have long oval heads, with numerous 
small shields (loreals) between the ocular and nasal 
() The students should work carefully over this section, comparing the specimens in 
the School Museum, a8 it is important for them to be able to recognise a poisonous snake 
when they come across one. 
