VERTEBRATA REPTILIA. 41 



secretions from which they anoint their feathers, and thus 

 ^render them impervious to moisture. 



41. Development. Birds are oviparous (Lat. ovum, an 

 egg ; pario, I bring forth) animals. The ovary is situated 

 011 the left side. During the passage of the egg through 

 the oviduct, it receives, first, the " white " or albuminous 

 covering with which the embryo is nourished; and, after- 



rds, the calcareous shell, with which it is covered. 

 From the oviduct it reaches the cloaca, and passes thence 

 to the outer world. It is then subjected for a longer or 

 shorter period to a process of incubation, by which the 

 chick is fully developed. To enable it to break the shell, 

 the bill of the young bird is provided with a protuber- 

 ance of calcareous matter, which afterwards disappears. 



Those birds which have been termed Autophagi (Gr. 

 dittos, self ; pJiago, I eat) are able to run about and provide 

 for themselves, as soon as they leave the shell. The other 

 section, Heterophagi (Gr. heteros, other ;phago, I eat), come 

 from the egg, blind and naked; and require to be protected 

 from cold, and fed by the parent birds for a considerable time. 



CLASS III. Eeptilia. 



42. The Reptilia (Lat. repto, I creep) form the third 

 class of vertebrate animals, and the second of the section, 

 Sauropsida. This class includes crocodiles, lizards, 

 serpents, turtles, and tortoises. 



They possess the following characters in common with 

 birds : They are oviparous, or ovoviviparous, animals ; 

 the embryo is provided with the membranes termed 

 amnion and allantois ; there are no mammary glands ; 

 at no period of life are gills present ; the skull is joined 

 to the vertebral column by a single occipital condyle ; 

 each half of the lower jaw consists of several pieces ; the 

 lower jaw is not united directly with the skull, but to an. 

 intervening quadrate bone ; the alimentary canal termi- 

 nates in a cloaca ; the red corpuscles of the blood are oval 

 in shape and contain a central solid particle or nucleus ; 



