442 MIGRATORY THRUSH. 



the epithelium tough, reddish-brown, with three longitudinal rugae on 

 one side, and four on the other. The proventricular glands very small, 

 forming a belt 5 twelfths in breadth. The contents of the stomach are 

 remains of insects, with a few particles of quartz. The intestine is 10 

 inches long, its width from 3;^ twelfths to 2 twelfths ; the coeca ex- 

 tremely small, 1^ twelfth in length, ^ twelfth in breadth, 1 inch dis- 

 tant from the extremity ; the cloaca oblong, 5 twelfths in breadth. 



The trachea is 2^ inches long, flattened ; 2 twelfths broad above, 

 1^ twelfth below ; its rings firm and rather broad, 60 in number, with 

 2 dimidiate rings. Bronchi short, of about 12 half rings. The muscles 

 as in the Mocking Bird and other Thrushes and Warblers. 



AMERICAN ROBIN OR MIGRATORT THRUSH. 



TURDUS MIGRATORIUS, LlNN. 



PLATE CXXXI. Vol. II. p. 190. 



The extent of migration of this bird, and its breeding from the 

 Texas to the 56th degree -of north latitude, and from the Atlantic 

 coast to the Columbia River, seem to me to afford a strong argument 

 against the necessity of migration in birds. In countries, like ours, of 

 great extent and varied climate, migrating birds find many favourable 

 places at which to stop during the summer months for the purpose of 

 breeding. I have repeatedly mentioned that young birds regularly ad- 

 vance farther southward in winter than their parents, which may be ac- 

 counted for by the capability of enduring cold being greater in the latter. 

 Now, is it not probable that young birds of a second or third brood, who 

 are tirged at an earlier period than those of the first set, but late in the 

 season, to force their way southward, and save themselves from the ri- 

 goxirs of approaching winter, are at this period of weaker constitution 

 than those which have been born earlier, and have been less pressed by 

 time in prosecuting their journey southward.'' In consequence of this, 

 the last young broods may be unwilling, perhaps unable, on the approach 

 of spring, to start and follow their stronger companions to the land of 

 their nativity. They may thus remain and breed in their first year's 

 winter quarters, or advance so far as their strength will allow them.^ 



