182 CRYSTALS OK CARBONATE OF LIME IN THE EGG-SHELL OF REPTILES. 



I am unable, at present, to obtain access to the original paper of M. 

 Turpin, and therefore, to ascertain whether he examined particularly the 

 egg-shell of the alligator ; but I infer that, as one of the reptiles, his 

 observation equally applies to that animal. 



Some eggs of the alligator having recently been given to me, I was 

 curious to examine the structure of the shell, and I was much surprised, 

 knowing what M. Turpin had written on the subject, to detect in them, 

 what appeared to me, decided indications of a crystalline arrangement. 



The egg-shell of the alligator consists of two layers. The inner is 

 thin and flexible, not at all crystalline, and indeed seems to be merely 

 the inner membrane dried. 



The outer layer is thicker and stronger than the former. Its exterior 

 is smooth, and its interior studded with minute eminences, visible to the 

 naked eye. These appearances may be seen in the following manner : 



1 . If the light be allowed to fall obliquely on the thin broken edge 

 of this layer, minute shining points, or facets, are seen here and there, 

 with the assistance of a single lens of low power,* or, still better, with 

 the higher power of a compound microscope. 



2. When viewed as an opaque object, with an achromatic power of 

 about fifty linear, the inner surface is seen to consist of an irregular 

 semi-transparent mass, having quite a crystalline appearance, although 

 no regularly formed crystals can be perceived. Among the minute 

 eminences above mentioned, many slender white fibres are seen, look- 

 ing much like acicular crystals, but which are not, I think, really such. 



3. The crystalline structure is best seen, by carefully crushing a por- 

 tion of the outer layer in a mortar, and then examining the powder as 

 an opaque object, on a dark ground, with a power of about fifty linear, 

 or more. The particles are clear and transparent, almost like crystal ; 

 they are not amorphous, but have a great tendency to break into more 

 or less regular fragments, bounded often by straight lines, and the frac- 

 tures are clear and shining. 



Although I have not been able to discover the regular rhomboidal 

 crystals which M. Turpin has elsewhere detected : yet, I think it is 

 proved by these observations, that the substance of the egg-shell here 

 spoken of consists of particles of carbonate of lime, so disposed as to 

 form not an amorphous mass, but a crystalline structure, such as we see 

 in loaf-sugar, white marble, &c. The inside shell is almost entirely 

 animal matter, and leaves but little residuum when burnt upon platinum. 



It is with the greatest diffidence that I advance an opinion in any 



* A Coddrington lens of thirty linear. 



