Various Modifying Agencies. 139 



Food. 



As examples of direct anatomical modification by food-habit, may be 

 mentioned the conversion of the gizzard or hard stomach of birds into a 

 soft stomach, and vice versa. The gizzard of the Pigeon is changed to 

 a soft stomach by a continuous diet of flesh ; while the soft stomach of 

 a Sea-gull has been changed to a tough, gristly gizzard, by feeding on 

 grain for a year. The Herring-gull in winter lives on fish, and has then 

 a soft stomach, but in summer it lives on grain and its stomach changes 

 to a gizzard, it has also been observed in a Raven and a species of Owl, 

 that the internal coats of the stomach change twice a year to suit their 

 food. The habits of some animals have been fixed for so many genera- 

 tions, and their anatomical structure has become so conformed to the 

 habits, that to change radically from their accustomed food would be 

 death to them. But food is food, and, if time enough be given, any 

 change can be wrought. The lion could, in the course of generations, 

 be made to eat straw like an ox, and the horse to relish fried oysters. 

 As it now is, the various animals are habituated to special lines of diet, 

 which, in certain cases, are very narrow. Some live on a particular ar- 

 ticle of animal food or vegetable food, others on a general class of ani- 



>1 or vegetable food, and siill others on a mixed diet. 



Jhe food has acted upon the animal structure, that it has habitually 

 nourished, directl}", in forming and fixing anatomical peculiarities, and 

 at the same time establishing the mental characteristics corresponding 

 to them. The character of the food first affects the stomach, an example 

 of which is given in the case of the modification made in birds by 

 changing from flesh to grain. The stomachs of animals in general dif- 

 fer from each other and correspond in form with the demands of the 

 digestive function, whatever that may be. 



The herbiverous animals, as a rule, have larger stomachs and longer 

 intestines than the carnivorous, because the quantity of vegetable food 

 required is much greater, as a rule, than that of animal food to produce 

 the same amount of tissue nourishment or heat. The ruminants, or 

 cud-chewers, eat enormous quantities of bulky grass, and have stomach 

 capacity to correspond. In fact, they have four stomachs; viz., paunch, 

 honeycomb, manyplies and rennet. The food goes in part into the 

 honeycomb, but mostly into the paunch, which, in the adult animal, 

 is an immense bag. It is relatively small in the young, and is only 

 developed by the bulk of food it receives. From the paunch the food 

 goes into the honeycomb or reticulum, and passes back and forth from 

 one to the other, and between them is macerated into a semi-fluid mass, 

 mixed with saliva. It is carried up from there in boluses back to the 

 mouth to be farther chewed nnd salivated. On its return, it flows over 

 the more solid, loss fluid, michcwed portions into the manyplies, and 



