418 WHITE-BELLIED SWALLOW. 



In the first part of August, they collect in large flocks about ten days 

 before their departure for warmer climates. During that time they 

 are to be seen in great quantities flying around and over the houses in 

 Boston in quest of insects." 



My friend Dr Bachman says, " On the afternoon of the 16th of 

 October 1833, in company with Dr Wilson and Mr John Woodhouse 

 Audubon, I saw such an immense quantity of this species of birds 

 that the air was positiAJ^ely darkened. As far as the eye could reach, 

 there were Swallows crowded thickly together, and winging their way 

 southward ; there must have been many millions !" 



The eggs of this bird measure five and a half eighths of an inch in 

 length, and half an inch in breadth. 



In an individual preserved in spirits, the length to end of tail is 5;^ 

 inches, to end of wings 5^, to end of claws 3i§ ; wing from flexure 4:^^ ; 

 tail 2i| ; extent of wings 12^. 



The roof of the mouth is flat, and of the same general description 

 as in the Purple Martin ; its width 4^ twelfths ; the tongue 3 twelfths 

 long, its point slit. Between each branch of the lower jaw and the 

 membrane of the mouth is a narrow oblong salivary gland, with two 

 ducts, opening near the junction of the branches. The oesophagus is 

 2 inches long, from 1^ twelfth to 1 twelfth in width ; the proventricu- 

 lus 2 twelfths. The stomach is irregularly elliptical, 6 twelfths long, 

 5i twelfths broad ; its structure as in the other species ; the epithelium 

 longitudinally rugous, reddish-brown. The intestine is 6 inches long, 

 from 2 twelfths to 1^ twelfth in width ; the cceca are 3 twelfths long, 

 and ^ twelfth in breadth, 1 inch distant from the extremity ; the cloaca 

 oblong, 4 twelfths wide. 



The trachea is 1 inch 4 twelfths long, considerably flattened ; its 

 rings pretty firm, 58 in number, with 2 dimidiate rings ; the muscles 

 as in the Purple Martin ; the bronchial half rings 15. 



In the structure of the mouth the Swallows are allied to the Fly- 

 catchers on the one hand, and to the Goatsuckers on the other. Their 

 digestive organs do not differ materially from those of the former. The 

 elongated narrow salivary gland found in all the species examined, occurs 

 equally in the Flycatchers, as well as in many other insectivorous birds ; 

 but is not larger in the species of which the materials of the nest are 

 fastened together by a gluey substance than in the rest. Although not 

 mentioned in the description of the Sand Martin, it occurs in it also. 



