172 Dr. Dickie on the Structure of the Shell of the 



from that in the grooves, but the small morsel of shell at my 

 disposal prevented me from fully ascertaining this. 1 have not 

 met with any other instance in which the epithelium presents a 

 structure so decidedly cellular as in the former of the two above 

 mentioned ; still there are some in which there can be no doubt 

 as to the nature of the tissue, the cells being, however, less di- 

 stinct and rather irregular in size and form ; as examples may 

 be mentioned the guillemot, missel thrush, land rail, common 

 grouse, redstart, greenfinch, &c. I have met with several in- 

 stances in which the cellular structure of the superficial layer is 

 not so evident, as in the blackbird, hedge-sparrow, chaffinch, 

 common lark, &c. I am indebted to Mr. Strickland for an oppor- 

 tunity of perusing remarks on Oology by M. Des Murs, published 

 some years ago. He speaks of the connexion between the ap- 

 pearance of the surface of the egg and the habits of birds and 

 the climates in which they permanently reside, or in which they 

 pass the breeding-season. He alludes to those of aquatic birds 

 generally as having a shell, whose surface is usually unpolished ; 

 in some, as the cormorants and others, the superficial layer is 

 easily detached. I may mention as an instance of this, the egg 

 of the Carbo Floridanus ; the surface is rough and without gloss, 

 and appears as if it had been white- washed. This is owing to 

 the nature of the epithelium, which is strong and composed of 

 numerous crowded granules and cells. The use of an acid is not 

 necessary for the separation of this epithelium, for if the surface 

 of the egg be moistened, the superficial layer may be peeled off 

 in pieces of considerable size. The fragments thus separated 

 effervesce strongly with acid, and require its application previous 

 to the use of the microscope, proving that in this instance at 

 least, a quantity of calcareous matter is deposited in the epithe- 

 lium and not in the fibrous layer only. A perpendicular section 

 of the shell in this particular case shows that the thick epi- 

 thelium with its calcareous deposit forms about one-fourth of the 

 entire thickness. The egg of the Ardea Herodias (Linn.), like 

 that just mentioned, has a superficial layer which may be easily 

 removed ; it will be found to contain calcareous matter, and in 

 some cases I have seen this deposit arranged in radiating crystals, 

 presenting an appearance like that observed by Dr. Carpenter in 

 the tooth of Mya arenaria, and compared by him to radiating 

 arragonite or wavellite. 



Des Murs alludes to a remarkable example, and, as he says, 

 unique in the entire family of birds denominated terrestrial or 

 non-aquatic : the case mentioned is that of the egg of the Croto- 

 phaga Ani ; the surface is rough and covered with a chalky layer, 

 on detaching which the egg is of a deep blue. 



The nucleus of the epithelium cells is usually absent ; it is 



