68 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



grain, and he thus succeeded in so completely hardening the 

 inner coat of the bird's stomach, which is naturally soft and 

 adapted to a fish diet, that in appearance and structure it pre- 

 cisely resembled the hard horny skin of the gizzard of a pigeon. 

 Dr. Edmonstone assures us that this experiment is annually 

 repeated by nature ; that the herring-gull Larus tridactylus 

 of the Shetland Islands twice every year changes the structure 

 of its stomach, according to its food, which consists during 

 the summer of grain, and during the winter of fish. This 

 gull then has, in fact, during the summer the stomach of a 

 grain-eater, and during the winter that of a carnivorous bird of 

 prey. The same naturalist observed a similar transformation 

 in the structure of the stomach in the raven, and Menetries 

 makes a similar statement with regard to an owl Strix 

 grallaria. 



These experiments suffice to prove that the stomach of a 

 carnivorous bird (an owl, a gull, and a raven) can be trans- 

 formed to that of a grain-eater if supplied for a sufficiently long 

 period with the food requisite for this result. The question then 

 obviously suggests itself whether the converse is equally true, 

 i.e., whether the gizzard of a true grain-eating bird can be 

 transformed into the soft-skinned stomach of a carnivorous 

 bird. The experiments of Dr. Holmgren in fact prove that in 

 pigeons which are fed on meat for a sufficiently long period, the 

 gizzard is gradually transformed into a carnivore vis stomach. 14 



I have not been able to collect a larger number of really 

 credible or experimentally proved data, and I believe that I 

 cannot have overlooked many really important and available 

 communications. I except, of course, the cases briefly given in 

 Note 15 of the influence of nutrition on sexual maturity and 

 on the secondary sexual characters of domestic animals, since 

 we are not justified in directly applying the results derived 

 from the artificially bred races of domestic animals to all others 

 living wild. Meagre as is the list here given, it amply suffices 

 to prove that changes in nutrition are able to exert even a direct 

 influence on many structural relations of organs, although it 

 must be admitted that we know nothing absolutely nothing 

 of the limits of the variations called forth by this direct influence 



