FOOD AND ITS UTILISATION 103 



proventriculus) and a posterior muscular portion (the 

 gizzard). John Hunter's experiment with a Herring Gull 

 showed that after a year's feeding on grain, the stomach 

 had become like a pigeon's gizzard. According to Edmond- 

 stone,the Herring Gull of the Shetlands changes the structure 

 of its stomach twice a year, according to its food, which 

 during the summer consists very largely of grain, and 

 during the winter of fish. Semper notices in his " Animal 

 Life" (1881, p. 68) that Edmondstone observed a similar 

 change in the raven, and Menetries in the owl {Strix gral- 

 laria), while Holmgren made the converse experiment of 

 feeding pigeons for a long time on flesh, with the result 

 that their stomach became like that of a carnivorous bird. 



These cases are very interesting because they illustrate 

 the process of somatic modification in the individual. A 

 change in the food is followed by a change in the structure. 

 In the flesh-eating bird the wall of the stomach shows 

 relatively little musculature and a strong development of 

 glandular tubules secreting the digestive juice. In the 

 grain-eating bird the musculature is particularly strong, 

 and instead of the soft mucous membrane there is in the 

 posterior region or gizzard the formation of a strong brown 

 lining, with long filaments extending into the cavities of 

 the tubules which run at right angles into the muscular 

 layer. The proventriculus remains like the stomach of a 

 carnivorous bird, with soft mucous membrane and glands. 



Semper writes (1881, p. 414) : " If the stomach of the 

 pigeon is acted on for a sufficiently long period by feeding 

 on flesh, the brown layer (called a cuticula) v/ithdraws 

 entirely from the tubules and is ejected ; the tubules 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 tubules in 

 the gizzard is to be compared, chemically and with respect 

 to its digestive 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 



