Conchology. 141 



receive new additions of matter, and increase in volume, These 

 indeed afford sufficient characteristic marks for a natural division 

 of bodies into two classes, namely, organized, and inorganized sub- 

 stances. 



The experiments of Reaumur have decisively proved, that the 

 growth of shells is owing to the latter mode of increase. These 

 experiments were made not only on sea shells, but also on land 

 and river shells; on univalves and bivalves; and, in all, the result 

 was invariably the same. In conducting these experiments, he 

 inclosed the shells, on the progress of which he made his observ- 

 ations, in boxes pierced with small holes so as to admit the wa- 

 ter, but so small as to prevent the egress of the animal. These 

 boxes were sunk in the sea, or the river, and in this way he was 

 enabled to watch the process of the growth of the shell. He first 

 observed, that when the animal, which exactly fitted its shell, be- 

 gan to increase its size, the shell in a short time, not being suffi- 

 ciently large to cover its whole body, part of it was naked or un- 

 protected. This part of the animal must always be towards the 

 opening of the shell, because the shell being previously complete- 

 ly filled, it cannot extend in any other direction. All animals 

 which inhabit shells of a spiral form, such as the snail and volute, 

 can only extend at the head, or the opening of the shell; whereas 

 the animals in bivalve shells, such as the muscle and the oyster, 

 may enlarge in their whole circumference. In all the species of 

 testaceous animals, it is this part which appears by the increase 

 of the animal when it enlarges the shell. This increase takes 

 place, according to Reaumur, by the following mechanism. 



It is a necessary effect of the laws of motion, when liquids run 

 in canals, that the small particles of these fluids, or the small for- 

 eign bodies mixed with them, which on account of their figure, or 

 their less degree of solidity in proportion to their surface, move 

 slower than the others, fly off from the centre of motion, and ap- 

 proach towards the sides of these canals. It even frequently hap- 

 pens, that these small particles attach themselves to the internal 

 surface of these canals or tubes, and form concretions of differ- 

 ent degrees of thickness. It is besides certain, that the fluids 

 which circulate in these tubes, press against their sides on every 

 point of their interior surface; so that if they were pierced with a 

 number of small holes of sufficient dinmeter to give passage to the 

 small particles of matter floating in these fluids, these particles 

 would be deposited on the external surface where a crust would 

 be formed similar to that of the inside; with this difference, that 

 it would become thicker and more solid, being less exposed to 

 the friction of the fluid, than that which is deposited in the inte- 

 rior of the tube. 



