GENERAL CHARACTERISTICS 3293 



Mollusks form a large item in the food of many mammals, birds, reptiles, and 

 fishes. Terrestrial forms are devoured by rats, ducks, thru.shes, and other birds; 

 by lizards, toads, snakes, and even by certain kinds of carnivorous insects. The 

 fresh-water forms are consumed in vast quantities by water birds of 

 esi " a ^ re every description, by fishes, frogs, water voles, and other mammals, 

 and aquatic creatures of various kinds; and every seashore is con- 

 stantly ransacked by flocks of sea fowl for the repasts of shellfish it affords. Out 

 in the depths of the ocean many kinds of fishes, especially cod, haddock, gurnard, 

 soles, and mullet, are great devourers of mollusks, which ever fall a prey, not only 

 to one another, but also to crabs, holothurians, sea anemones, and starfishes; and, 

 finally, among the pelagic pteropods the Greenland whale seeks his daily sus- 

 tenance. 



Mollusks of all kinds, but especially the marine species, are much eaten by the 

 natives of most countries; and even in Europe, although the oyster is the most 

 highly appreciated, several other species are used as food. Mollusks are not only 

 of importance to man as an article of diet, but they are serviceable in other ways. 

 Their shells are employed as personal ornaments, and are used in the manufacture 

 of fishing tackle by some uncivilized people. In England and other countries many 

 of the pearly species are manufactured into ornaments and various useful articles, 

 and the beautiful pearls themselves secreted within the tissues of the pearl oyster, 

 are esteemed as jewels. 



The utility of the mollusks to man probably far outweighs the injury 



which is occasioned by a few kinds. In the foremost rank of the 

 lusks 



noxious species stands the Teredo, the great destroyer of submerged 



timber. The damage done to piers, boat bottoms, and in fact to wood of any de- 

 scription which is located in the sea, is enormous, and there seems to be no effectual 

 means of meeting the attack of these mollusks, except by covering the timber with 

 metal sheeting. The stone work of breakwaters occasionally become more or less 

 damaged by the burrowing habits of the Pholas and Saxicava. On land, snails and 

 slugs commit onslaughts upon our crops and gardens, but these pests are more easily 

 overcome than their marine relatives. 



Although this is a subject very fascinating to some, it is one which 

 Distribution ... ,, , ... , . , 



pre-eminently opens the gates of speculation. That species have cer- 

 tain geographical and bathy metrical limits in their distribution, may be an admis- 

 sible fact in very many cases, but when the reason for this limitation is sought we 

 are reminded how little we know of natural causes. That certain tracts of coast 

 have their own peculiar inhabitants, and that the mollusks of the eastern shores of 

 America, for example, differ from those of the west we must admit; but how this 

 has come about, is matter of conjecture. We say that differences of environment, 

 of food and temperature, are sufficient reasons to account for such things. On the 

 contrary, we are met with the fact that certain species in a given genus have a much 

 wider range than others, and we are fain to ask how this is brought about. The 

 range of terrestrial mollusks is much more restricted than that of most marine forms. 

 This is readily understood, as the means of dispersal are very different. The early 

 stages of marine mollusks, if not free-swimming creatures, are liable to be carried 



