EXTERNAL CHARACTERS. 425 



hence commence to develop before they are laid. The egg 

 contains within itself sufficient nutriment for the develop- 

 ment of the chick up to the time of hatching : and all that 

 IS necessary to ensure development is that the egg, after it is 

 laid, should be kept at about the temperature of the parent's 

 body. This is in most birds effected by incubation, a task 

 usually fulfilled by the hen bird, but sometimes wholly or 

 in part by the cock. 



The food of the pigeon consists largely of hard seeds, and 

 small stones are swallowed with it. 



Pigeons should be killed with chloroform, otherwise the 

 lice with which they are invariably infested may prove a great 

 nuisance. Before the dissection is commenced, the bird should 

 be thoroughly plucked, with the exception of one of the wings, 

 on which the feathers may be left till later. 



I. EXTERNAL- CHARACTERS. 



Excepting the lower joints of the legs and the toes, nearly 

 the whole surface of the body is covered with feathers. 



A. The Main Divisions of the Body. 



1. The head is elongated antero-posteriorly, and produced 



in front into a pointed horny beak. 



At the base of the beak is a naked swollen patch 

 of skin, the cere. 



At the sides of the head are the large eyes, each 

 provided with upper and lower lids, and with a well- 

 developed third eyelid, or nictitating membrane, a 

 semi-transparent fold of skin which can be drawn 

 across the eye from its anterior angle with great 

 rapidity. 



2. The neck is very long and flexible. 



3. The trunk is deep dorso-ventrally, and somewhat com- 



pressed from side to side. Along the mid- ventral 



