116 AYES. 



modifications. The superior larynx, which is extremely simple, has but 

 little to do with it. 



The horny substance which invests the two mandibles performs the 

 office of teeth, and is sometimes so jagged as to resemble them ; its form, 

 as well as that of the mandibles which support it, varies extremely, and 

 according to the kind of food used by each species. 



The digestion of birds is in proportion to the activity of their life, and 

 the force of their respiration. The stomach is composed of three parts : 

 the crop, which is an enlargement of the oesophagus ; a membranous 

 stomach, in the thickness of whose parietes are a multitude of glands 

 whose juices moisten the aliment ; and finally, the gizzard, armed with 

 two powerful muscles, united by two radiated tendons, and lined inter- 

 nally with a kind of cartilaginous velvet. The food is the more easily 

 ground there, as birds constantly swallow small stones, in order to in- 

 crease its triturative power. 



In the greater part of the species which feed exclusively on flesh or 

 fish, the muscles and villous coat of the gizzard are greatly attenuated ; 

 and it seems to make but a single sac with the membranous stomach. 



The dilatation of the crop is also sometimes wanting. 



Tlie egg, detached from the ovary, where it consists merely of yolk, 

 imbibes that external fluid, called the white, in the upper part of the 

 oviduct, and becomes invested with its shell at the bottom of the same 

 canal. The chick contained within it is developed by incubation, unless 

 the heat of the climate suffices for that purpose, as is the case with the 

 egg of the ostrich. The young bird has a little horny point at the ex- 

 tremity of the beak, with which it splits open the shell, and which falls 

 off a few days after it is hatched. 



The industry and skill exhibited by birds in their variously constructed 

 nests, and their tenderness and care in protecting their eggs and young, 

 are known to every one ; it is the principal part of their instinct. Their 

 rapid transitions through different regions of the air, and the vivid and 

 continual action of that element upon them, enable them to anticipate 

 atmospheric changes, to an extent of which we can form no idea ; and 

 caused the ancients, in their superstition, to attribute to them the power 

 of prescience or divination. It is unquestionably on this faculty, that 

 depends the instinct which acts upon the birds of passage, prompting 

 them to seek the south on the approach of winter, and the north on the 

 return of spring. They have memory, and even imagination for they 

 dream. They are easily tamed, may be taught to render various ser- 

 vices, and retain the air and words of songs. 



