OF EASTERN PENNSYLVANIA, 07 



and old retire to their winter quarters in Mexico, Central 

 America, and the northern parts of South America. 



The eggs are elliptical in contour, and equally obtuse at 

 each extremity. Their ground-color varies, being different 

 shades of stone-color : in some, a dirty white ; in others, a 

 clay-color; and, again, in others of a yellow or blue tinge. 

 The markings, which are varying shades of yellowish-brown 

 and slate, are pretty generally diffused over their entire sur- 

 face. Their resemblance to oblong-oval, dark-colored peb- 

 ble-stones, is so accurate, as readily to deceive the most acute 

 observer. This resemblance is very much heightened by 

 the small stones among which they are not uncommonly 

 placed. It is evident from the foregoing facts, that their 

 safety is in a great measure dependent upon these natural 

 surroundings. Specimens vary in length from 1.28 to 1.12 

 of an inch, and in breadth from .82 to .93 of an inch. 



Family Cypselidse. Swifts. 



In these fissirostral Pica-rite, the bill is quite small, flatten- 

 ed, and presents a triangular outline when viewed superiorly : 

 it is remarkable for its immense gape which reaches below 

 the eyes. The wings are extremely elongated, often as long 

 as the entire bird, thin and pointed ; the secondaries very 

 short, and probably nine in number. The feet are small and 

 feeble ; the tarsi nude, or feathered ; the posterior toe, often 

 elevated, or versatile, or permanently turned towards the 

 side, or even forwards : the front toes are perfectly cleft, with 

 extremely short basal phalanges, and very long penultimate 

 ones ; claws acute and curved, but never pectinate. The 

 sternum prominently keeled, widening posteriorly, and with 

 the hind margin entire. The great development of the sali- 

 vury glands is one of the most remarkable structural pecu- 

 liarities of the Cvpselidtc. The secretion of these glands 

 is of great service to these birds in nest-building, in all the 

 species whose nidificating habits are known. In the gener- 

 ality of cases, a gluey substance is formed, by which the 

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