BY D. EMBLETON, M.D. 55 



Professor Allen Thomson* says that '4n those instances in 

 which the shell of eggs is coloured the pigment substance of 

 various hues is generally deposited in cells, which are strewed 

 uniformly or in patches over the external surface of the calcare- 

 ous shell. In some other instances however the colour seems to 

 be merely a uniform tint of the outermost layer of calcareous 

 matter." 



These items of information are all that I have been able to 

 gather from books ; in the works of Temminck, Mudie, Yarrell, 

 Bewick, Macgillivray, Jones, jS'ewman, Morris, and Audubon, 

 the cause of the coloration of eggs is not mentioned, and Pro- 

 fessor Flourens, as has been seen, prefers the theory of a peculiar 

 secretion to that of emissions of blood, as that which would best 

 account for the coloration. 



In the works of those who have treated of eggs or their co- 

 lours, we find no description whatever of glands in the lining 

 membrane of the oviduct that might be supposed capable of se- 

 creting pigmentary matter, and it has not been demonstrated that 

 the colouring matter either of the ground colour or the spots is 

 contained in special cells. 



III. — An^atomy AisTD Physiology. — Before discussing the sub- 

 jects of the form and coloration of eggs, it will be useful to 

 notice briefly the anatomy and physiology of the reproductive 

 organs of the female bird, and the gradual building up of the egg. 



It is generally known that in birds the generative organs of 

 the left side only, as a rule, come to maturity of structure and 

 function, those of the right side remaining comparatively small 

 and inactive. f 



Of the accompanying Woodcuts, 'No. 3 is taken from Dr. 

 Thomson's Article ''Ovum," in Todd's Cyclopoedia of Anatomy 

 and Physiology, and No. 4 from Traito elementairc D'Anatomie 

 comparee par C. G. Carus, Paris, 1835. In both the ovarium, 

 with ova in various stages of development, is scon at the top, a, 

 and one of the points of the fringe of the funnel, h, at the top of 



* Cyclopoedia of Anat. and Physiol., Vol. V., Supploniciit, p. GIJ. 

 t 111 some of the Raptorial birds they present an equal development. Carpenter's 

 General and Comparative Principles of Physiology, 3rd Ed., p. 514. 



