154 TETRAO TETRIX. 



four inches. To obtain uniform measurements therefore, the 

 parts ought to be inflated. 



Habits. — If we take the digestive organs, with their functions, 

 as a point from which to set out in tracing the habits of this of 

 any other bird, we shall be enabled to present a more connected 

 account of them than is usually found in our most approved 

 works. Let us suppose that, early on a sunny morning in 

 October, excited by a peculiar sensation which we denominate 

 hunger, the Black Grouse is seen threading his way among 

 tufts of heath in some wild glen of the Grampians. By means 

 of its short, strong, sharp-edged bill, it picks off small portions 

 of the fresh twigs of Erica cinerea, Calluna vulgaris, Yaccinium 

 Myrtillus, Willows, and other shrubs, with which, and occa- 

 sionally other substances, such as berries of Vaccinium Vitis- 

 idsea, Vaccinium Myrtillus, and Empetrum nigrum, and leaves 

 of various plants, it gradually fills its crop, which is capable of 

 containing a very large quantity, in fact a globular mass from 

 three and a half to four inches in diameter. These twigs are 

 all cut of a length not exceeding half an inch, arrive in the crop 

 slightly moistened, and remain there for a time without ap- 

 parently undergoing any other change than that of being in a 

 small degree moistened. A quantity passes into the gizzard 

 until it is filled, when it is acted upon by the powerful muscles 

 of that organ and its cuticular lining, of which the action is 

 aided by numerous fragments of quartz, many of which, by 

 long use, are often rounded and polished. The crude food 

 passes down the oesophagus in the form of a compact cylinder, 

 completely filling it, sliding along its lubricated surface, and in 

 passing through the proventriculus receiving a quantity of fluid 

 from its glands. In the gizzard it presents the same form, im- 

 pressed with the rugae of the inner coat, and being intimately 

 mixed with the fragments of quartz, is triturated into a coarse 

 pulpy but slightly moistened mass, in which state it enters the 

 intestine by the pylorus, which seems to have the power of re- 

 jecting the mineral particles, as none of them are ever found 

 beyond the stomach. In the upper or duodenal part of the in- 

 testine it is diluted with the pancreatic and biliary fluids, and 



