EY D. EMBLETON, M.D. 53 



present subject, are thus given: *'As to the colour and mark- 

 ings of eggs, that these are very various, that the colouring 

 matter is of an organic kind, very similar to that of leaves and 

 flowers, and in part depends on molecular arrangements." 



In the short discussion that followed the reading of the paper, 

 I expressed myself as not satisfied with Dr. Davy's explanation, 

 and offered the opinion ''that the coloration of eggs of birds 

 occurred during their passage down the oviduct to the exterior, 

 and was due to the effusion of blood in varying quantities from 

 the capillary vessels of the mucous membrane of the oviduct ; 

 and that the blood so effused was acted upon, as by a mordant, by 

 the plastic matter thrown out for the formation of the shell, and 

 that its colour thus became fixed, that in fact the process of the 

 coloration of eggs is a species of natural fresco-painting." 



Since the above date this subject has seldom been referred to 

 by me. Only lately, indeed, and as a pastime at spare moments, 

 in the intervals of professional duties, have I been able to put 

 into its present form what has since been observed. And it will 

 be seen that I hold the same opinion as before with respect to 

 the markings on eggs being caused by effused blood ; but I was 

 at that time unaware of the fact that the blood, after effusion, 

 underwent any chemical change, nor had it occurred to me what 

 might possibly be the cause of their uniform ground colour. 



In books on Ornithology, or on Oology, we find little else than 

 conjectures as to the origin or cause of the markings in question. 



Dr. Erasmus Darwin,^' in his Zoonomia, referred to by several 

 authors, ascribes the origin of the colours of eggs to the colours 

 of the objects among which the mother bird chiefly lives acting 

 upon the shell through the medium of the nervous system. 



His concluding words are these, ''and finally, that colours 

 may thus be given to the egg-shell by the imagination of the 

 female parent." 



Knappf states, "That in the eggs of one hue the colouring 

 matter resides in the calcareous part, but when tliore are mark- 

 ings, these arc rather extraneous to it than mixed with it. The 



* Zoonomia, Sect. ."!), p. 511. 2ml ImIU. London, 1794. 

 t .louiMml of a Naturalist, p. '-';;. 



