322 GEORGE W. BARTELMEZ. 



it is necessary to call to mind these characters and their relations 

 to one another. 



The two ends of the principal egg axis are differentiated by 

 the following characters: 



1 . The relation of the embryo to the principal axis is such that 

 its right side is nearer one end of this axis, its left side nearer 

 the other. 



2. Shape of Shell. The two ends of the shell differ from one 

 another in the eggs of most birds so that we may usually speak 

 of a blunt and a pointed end. 



3. Pigment. The eggs of many birds, particularly among the 

 Passeres are more or less spotted with pigment. The character- 

 istic flecks, blotches, streaks or lines are often unequally dis- 

 tributed over the shell so as to differentiate between the two 

 ends of the principal axis. Sometimes there is a pigment wreath 

 around the blunt end as in many warblers, sometimes the spots 

 are irregularly scattered over the blunt end as in certain fly- 

 catchers and in still others there are spots over most parts of the 

 shell but they are more abundant over the blunt end (certain 

 warblers), and finally in some heavily pigmented eggs like those 

 of the English sparrow the pigment is scantier at the pointed 

 end than elsewhere. The reason for this is obvious when one 

 considers the mode of origin of this pigment and the orientation 

 of the egg in the oviduct (cf. p. 333). This character, then, 

 is a well-defined differentiation of the long axis. 



4. Air Space. In the laid egg the air space is always at or 

 near the blunter end of the shell. This is an exceptionally 

 constant character. 



5. Chalazce. The chalazse are normally attached to the yolk 

 in the line of the principal axis so that the chalazal axis is merely 

 another expression of this axis. Furthermore, one often finds 

 that one chalaza is larger and more distinct than the other. 

 It is almost invariably the one at the pointed end of the shell. 

 During incubation the blunt end chalaza is more likely to become 

 detached or to disappear entirely; that is to say it reverts more 

 readily to the sol phase. 



6. Ligamentum Albuminis. The second or thicker albumen 

 is more or less firmly attached to the inner shell membrane, 



