178 



INTRODUCTION TO ZOOLOGY. 



object of procuring food. This consists of sea-weeds of 

 different kinds, which it rasps down by means of a ribbon- 

 shaped instrument longer than its entire body, and covered 

 with minute recurved hooks. The first time we chanced to 



Fig. 1G5. LIMPET.* 



Fig. 1GG. CHITON. 



see this, we mistook it for some strange species of worm ; but, 

 on examining several Limpets, the supposed worm was seen 

 in all ; and great was our astonishment when we discovered 

 that we had, in every case, been looking at the tongue of the 

 Limpet, and not at any intruder into the privacy of his conical 

 fortress. 



The shell of the Limpet consists of one piece ; but in the 

 Chiton (Fig. 166), an allied genus found near low water- 

 mark, and under stones, the shell is composed of a number 

 of distinct plates. These are so arranged that the edges 

 overlap -like the slates of a house, and the ligaments possess 

 such flexibility, that the shell can, at the pleasure of the 

 animal, be rolled into a ball. 



That order which is characterised by having the gills 

 concealed under a fold of the mantle (Tectibranchiata) may 

 be illustrated by reference to a creature not uncommon on our 

 shores, the Aplysia or Sea-hare, the Lepus marinus of the 



* Fig. lf>5. The animal of the Limpet, as seen from below. 3, Head. c, 

 Edge of shell. m, Mantle, b, Branchiae./, Foot. 



