Conchology. , 205 



the body of the animal on which they were formed, are hollow, 

 and during the remaining part of its existence, as the body en- 

 larges, they are partly hollow, and pajtly solid, being filled with 

 testaceous matter, excreted from the body of the animal, and then 

 the internal surface of the shell becomes smooth and even. 



Spines, and fringed or irregular protuberances, with which some 

 .shells are armed, have, according to all appearance, the same ori- 

 gin as the other inequalities on the external surface of shells. 

 They are usually formed at the end of the different successive pe- 

 riods of the growth of the shell. This will be sufficiently obvious, 

 if we trace the whole series of wrinkles or striee which run paral- 

 lel to the circumference of the opening. Those which arise im- 

 mediately from the ribs or varices, are produced by particular or- 

 gans which surround the extremity of the neck, and stretch out 

 from every part of its circumference, secreting a testaceous mat- 

 ter, which partly forms a sheath around them, gradually increases 

 in thickness, and successively assumes the form of that part of the 

 body which in some measure serves the purpose of a mould. In 

 all the species of murex, which are furnished with spines, the ele- 

 vation called the varices, or ribs as well as the spines with which 

 they are armed, are placed on the shell at equal distances, and the 

 intermediate parts of the shell, although frequently grooved or 

 striaeted, are not furnished with spines. 



This uniform observation, not only in shells belonging to this 

 genus, but also in almost all spinous shells, proves, that the spines 

 as well as the ribs, are to be considered as formed by the margin 

 of the anterior parts of the body, which is renewed in the same 

 proportion as the change in the position of this part of the body 

 takes place. It proves also, that the formation of shells is entire- 

 ly owing to the successive and regular enlargement of the animal; 

 and that it increases every time it is displaced from the whole ex- 

 tent in breadth of the anterior part of the body, the margin of 

 which, only being furnished with long, fleshy processes or fringed 

 appendices, is in reahty the only part which produces them on the 

 shell at each period of its increase. In the same way is formed 

 the beak or prolongation of the shell, which terminates the inferior 

 extremity in the form of a canal. This canal is produced in all 

 shells in which it exists, by a cylindrical organ, susceptible of ex- 

 tension and contraction, and which, according to some naturalists, 

 is employed by the animal as a kind of feeler, and occasionally to 

 attach itself to solid bodies. It excretes and deposits a testa- 

 ceous layer which serves it as a kind of sheath, in a similar manner 

 to the production of spines. 



It is easy to explain the formation of the grooves or elevated 



