58 M. Voit Buch oji the Silkification i)f' Organic Bodies. 



But I will return to the consideration of the oyster, for the 

 conclusion as to other shells will be easy, when we can shew, in 

 the case of the oyster, that the shell actually consists of calcare- 

 ous spar. 



When a person examines fossil oysters, the shells of which 

 are generally particularly thick, he finds without trouble lamellae 

 of such strength that the fracture of the profile can easily be in- 

 vestigated. On every side we see it to be fibrous, with thick 

 parallel fibres, which are placed at right angles upon the planes 

 of the lamellae. 



Oysters from the chalk at the lake of Berre, near Mar- 

 tigue, not far from Marseilles, show this structure very clearly. 

 When we look down upon them with the light of the sun, we 

 thus discover, by turning them in some directions, the very 

 small shining plates which the fibres surround, and towards 

 which they are considerably inclined. And these plates can 

 belong only to the rhomboedral calcareous spar, the principal 

 axis of which agrees with the axis of the fibre. And this is 

 what the law requires which regulates fibrous calcareous spar, 

 as well as every crystalline structure having the axes unequal. 

 Since the formation of the lamellae does not begin from a point, 

 and since the calcareous spar will be secreted in a similar 

 form upon the whole surface of the cloak of the animal ; so 

 the calcareous spar cannot construct fibrous tissues, stellularly 

 disposed. But the thin lamellae produced will resemble a cal- 

 careous pellicle, such as is separated from calcareous water, and 

 is deposited at the bottom. But such a calcareous pellicle is ex- 

 actly like the terminal planes of the perfect six-sided prism of 

 calcareous spar, and has the same appearance. This is an ob- 

 servation as fine as it is just, and has been made public by a 

 person unknown to me. 



We know that when six-sided prisms of calcareous spar are 

 quite transparent, this transparency never exists at the even 

 surface of the terminal planes. These are always muddy, 

 pearly and glimmery, hke slate-spar, (schieferspar). 



There are many small axes projecting from the surface, and 

 the small inequalities which arise therefrom reflect the light in 

 many different directions. 



We cannot believe that this structure probably belongs only 



