414 NOTES. 



theless able, and by their internal nature must be able, to accommodate 

 themselves to others. 



Note 13, page 64. It seems to me desirable to add a few more in- 

 stances of voluntary change of food by monophagous animals to those 

 given in the text. The palm-crab, Birgus latro, in a free state feeds on 

 fruits, namely cocoa-nuts, but in confinement eats its fellows (as I know 

 by experience). Canary birds, and fowls, often and readily eat lard. 

 The American prairie dogs Hans and Gretel, which I have already 

 mentioned in the text, quickly accustomed themselves to a diet of fish, 

 which was wholly unknown to them, with mollusca and meat. I owe 

 to my friend Professor Hagen (of Cambridge, Mass. U.S.) the following 

 interesting notes. At Cape Cod, the cows are regularly fed on herrings' 

 heads ; in Norway a mash is prepared for the cows by mixing and 

 stirring horse-dung with the heads of dorse boiled down ; this serves 

 them for fodder only in the winter ; in the summer they eat grass, as they 

 do everywhere else. The reindeer, according to Brehm, sometimes eat 

 lemmings. 



Note 14, page 68. The change of structure which takes place in the 

 stomach of the pigeon and the gull in consequence of the change of 

 function is as follows. The stomach of a bird subsisting on flesh has a 

 comparatively feebly developed muscular layer and a soft mucous mem- 

 brane, which penetrates the coats of the stomach, forming long tubules ; 

 these tubules are the glands which secrete the gastric juice. In the 

 grain- eating birds the muscles of the stomach are particularly strong ; 

 instead of the soft mucous membrane a thick brown membrane covers 

 the inner surface of the larger part of the stomach, while the small 

 anterior portion exhibits the same soft skin and glandular layer as are 

 everywhere distributed in the stomach of birds of prey. This brown 

 skin in the gizzard of the pigeon (see fig. 13) is very strong ; it has long 

 fine filaments which penetrate the cavities of the tubules which extend 

 perpendicularly into the muscular layer of the stomach. Now, if the 

 stomach of the pigeon is acted on for a sufficiently long period by feeding 

 on flesh, this brown skin (called a cuticula) withdraws entirely from 

 the tubules and is ejected : the tubules now no longer secrete any 

 solid matter, but only a fluid, and so become true glands. It would be 

 interesting to ascertain whether the secretion now. produced by these in 

 the gizzard is to be compared, chemically and with respect to its diges- 

 tive qualities, to the gastric juice in the stomach of birds of prey. In 

 gulls, on the other hand, which have become accustomed to a grain diet, 

 the hitherto fluid secretion from the glands opening into the stomach 

 becomes rigid, and a more or less firm thick skin is formed in the 

 interior of the stomach. 



From the text it might perhaps be inferred that the stomachs of 

 graminivorous and of carnivorous birds were two distinct forms of 

 stomach corresponding uniformly and exactly to these modes of feed- 



