EXCEPTIONAL STRUCTURE. 189 



which presents a marked exception to the ordinary 

 appearance of the eggs of birds, and assimilates 

 them, in some degree, to the sculptured eggs of 

 insects, only that the carvings in the latter exhibit 

 a greater regularity; they are also constant, while 

 these, in some cases at least, are exceptional. The 

 surface of the shell presents a granulated or sculp- 

 tured look, but there is that absence of regular 

 marking and configuration in the sculpturing which 

 indicates the fact of its being oftentimes accidental 

 in its origin ; the accident, however, of its produc- 

 tion, taking place before and not after its extrusion. 

 Sometimes the egg-shells of the titmice will pre- 

 sent a singular patch, or more patches than one, 

 of a yellow glistening varnish, as though some 

 painter had let fall a brush dipped in yellow var- 

 nish upon them. It appears difficult to account 

 for these varieties, and their occurrence must be 

 rather considered interesting than important. 



In every instance the shell is more or less per- 

 vious to air. In some of the instances detailed, 

 this property appears possessed in a higher degree 

 than in others ; but in all, the shell, however ap- 

 parently hard and compact, presents but little 

 difficulty to the ingress or egress of air through 



