100 KINSHIP OF BIRDS, AS SHOWN BY EGGS. 



as we have seen, were doubtless much later than egg depo- 

 sition, and it is hardly denied that these have done more to 

 influence egg coloration than anything else. Now to-day it 

 is known that few things are more variable than styles of 

 modification. Climate and environment often entirely revo- 

 lutionize building habits, not to notice the factor of variation 

 here as elsewhere. Herein we face the full force of migra- 

 tion on our subject, and halt in the presence of the fact that 

 physiological trends and habits that afifect the egg, both in 

 time past and present, were set up in a far northern climate, 

 in an environment now entirely changed and forever beyond 

 our knowledge. The modern birds have come out of an un- 

 known region, bringing with them their desire to get back — 

 and their eggs marked to suit the foreign surroundings. We 

 must feel that they have left behind many interesting phases 

 of their original modification. The bird which in the arctics 

 long ago may have lined its nest with green moss or gray 

 lichens may now floor it with flax in Dakota, or pad it with 

 cotton in Texas ; and yet in either deposit a solid green or 

 mottled grayish egg in keeping with the colors of " the old 

 house at home." So now unlimited tendencies to reversion 

 may set back. 



With regard to modern reversions the occasional white egg 

 now and then found, or entire white sets as noted among 

 the Hawk-forms may be a kind of albinism or abnormal 

 deficiency of color ; but this is not always necessarily the 

 case. 



It is well known that a bloom or chalky deposit character- 

 izes the eggs of many water birds — especially Grebes and 

 Cormorants, some Grouse, and noticeably the Cuckoos. 

 While it happens upon eggs of birds far apart it may in some 

 measure indicate kinship. The Coccygomorp/uz or Cuckoos 

 and GalUiice or Fowl groups are akin, according to Prof. 

 Huxley. But the peculiarity is most striking in the Pelican- 

 forms — whose affinities to other water birds are apparent 

 only to the anatomist. But this roughness of the shell is 



