6 
When scientists began more carefully to examine the struc- 
ture of shellfish, they found that those similarly constructed had 
shells with certain marked peculiarities. The days of conchology 
were then doomed; and the study of the mullusc, or malacology, 
took its place. 
Besides those necessary for digesting food, most shellfish have 
organs equivalent to those of vertebrate animals, such as feet, arms, 
eyes, head, heart, and tongue. Although bearing the same names, 
these organs rarely have a similar shape to those of the vertebrates, 
being necessarily adapted to the different mode of living. The 
foot of a cockle, shaped like an animal’s tongue, enables it to move 
slowly from place to place, as well as to burrow in a sandy beach 
with the comical jerks so well known to observers. The tongues are 
beautifully designed for their work. The long, narrow 
tongue of the vegetarian mollusc works like a scythe, and 
mows down the delicate marine grasses on which the animal feeds. 
The powerful tongues of those that prefer an animal diet are able 
to bore through the strongest shells; and woe betide the unfortunate 
shellfish which, having shown signs of weakness, or disease, is 
surrounded by its active, carnivorous brethren. The tongue, some- 
times longer even than the shell itself, is covered with rows of very 
hard spikes, or teeth, arranged similarly to the burrs on a file. As 
these teeth break, or are worn out, they are replaced by others that 
push themselves forward when wanted. Under a microscope of 
moderate power, the radula, or tongue, of a shellfish, especially a 
limpet, is a most interesting sight, and many molluscs can be 
identified merely by examining the tongue under a microscope. 
The shape of the teeth, the number, and the arrangement of them 
will settle the question. 
The appetites of molluscs verge on the voracious. Break 
up a few cockles, or other shellfish, and place them in shallow 
water on a calm day, and watch the result. If in the vicinity of 
rocks, and during a rising tide, all the better. First come the 
wary little shrimps to the feast. Some are creeping cautiously, 
and some are jumping and racing, as if afraid of not being in 
time. Then the carnivorous shellfish approach from all directions, 
foremost amongst them being the different species of Cominella. 
While they are lumbering along, shells appear to be actually 
running; but a close inspection shows that these contain active 
little hermit crabs, whose tender tails, having no hard covering 
of their own, are snugly stowed in the empty shells of defunct 
