COLOUR OF EGGS. 119 



shade of colour from nearly pure white to dark pur- 

 plish black, and yet all these varieties seem to be 

 equally thriving and untainted with disease, or what 

 the LinnaBari botanists are accustomed to designate 

 monstrosity. The case is the same with animals, 

 as may be shown, among numerous other instances, 

 in the banded snail-shell (Helix nemoralis). Within 

 the space of half a mile we have collected not 

 less than a dozen varieties of this species, having 

 from one band to seven, and the bands as diversified 

 in the shades of their colour as in their breadth and 

 arrangement, some being very pale and others of a 

 dark blackish brown. In the garden spider (Epeira 

 diadema) there is an equal diversity of markings and 

 shades of colour, some being bright orange, others 

 dark brown, and others greenish grey, while the spots 

 are sometimes large and conspicuous, and sometimes 

 small and indistinct*. The causes of this diversity 

 we have been unable to trace in a satisfactory manner, 

 though we have for many years paid considerable 

 attention to the subject ; we have mentioned it here 

 merely to introduce what we are about to say on the 

 subject of the diversity of colour in the eggs of birds, 

 by reminding the reader that the phenomenon, how- 

 ever obscure as to its final cause, is not unexemplified 

 in other natural productions. 



If we advert to the manner in which the shell of an 

 egg is formed, we may discover some of the circum- 

 stances attendant on the colouring and the markings. 

 The shell has been ascertained to be a secretion 

 whose basis is lime, derived from the glands of the 

 egg tube after the nucleus, consisting of the yolk and 

 white, has advanced from the egg-bag (ovarium). 

 The white colour of the eggs of the barn-door fowl, 

 the dull cream colour of those of the pheasant, the 

 greenish brown of those of the nightingale, and the 

 J. R. 



