MOLLUSCS. 77 



MOLLUSCS. 



Both in number of species and importance of forms the molluscs far 

 surpass any of the groups of animals so far enumerated in these pages. 

 Many of them, like the oyster and the clam, have an economic value ; 

 others, like the ship-worm and the ' drill,' are to be regarded as injurious. 

 wme furnish pearls, while the shells of others are of value as furnishing 

 the material for cameos. In ancient times it was molluscs which fur- 

 nished the celebrated Tyrian purple, while, in all probability, it is to the 

 squid, eaten by the sperm-whale, that the ambergris is to be attributed. 



The beauty and variety of the shells of the molluscs have rendered them 

 great favorites with collectors ever since the revival of letters, and two 

 hundred years ago every king had his cabinet of curiosities, in which shells 

 occupied possibly the most prominent place. As time rolled on, the fever 

 increased, and though it never reached the height of the tulip mania, still 

 rare shells were a safe investment and brought high prices, of course not 

 from any intrinsic value, but merely on account of their variety. Thus 

 two hundred years ago, the shell known as the precious wentle-trap sold 

 for forty pounds ; to-day it is worth but a dollar or two. Even within 

 twenty years some high prices have been paid for shells, sometimes fifty 

 dollars for a single specimen, and that not because the species was 

 extremely rare, but merely on account of a certain fashion. 



These various considerations have led to a great interest in molluscs 

 among scientific men which has evinced itself in an enormous literature, 

 possibly greater than that devoted to any other subject of natural history, 

 except birds and insects. Still, notwithstanding all the books and papers 

 relating to the group, our real knowledge of it is relatively small. The 

 species are well known, but more exact observations on the anatomy, 

 embryology, and physiology are greatly needed. 



The name Mollusc is derived from the Latin mollis, soft, and is descrip- 

 tive of a molluscan character which, while very desirable in an oyster, is 

 really of but little scientific importance. It is beyond our scope to enter 

 into exact definitions, but in order to render the following pages intel- 

 ligible, a few details are absolutely necessary. In the typical mollusc the 

 body is produced on either side into a broad flap which, from the way in 



