MANUAL OF NATURAL HISTOBY. 661 



parasitic species which bury themselves in the skin, 

 and which may be detected by the tumours they 

 produce, or by the holes they inhabit. 



The rocks must be keenly searched for Limpets 

 and Chitons, which frequently assume the colour of 

 their habitat, and require a practised eye to detect 

 them ; they must be taken by surprise, and sud- 

 denly lifted off by the point of a knife before they 

 can fix themselves firmly. The internal parts of the 

 Limpets can be simply removed, but the Chitons 

 must be placed in fresh water, their inside carefully 

 removed, and then strapped down upon thin strips 

 of wood ; tied to layers of talc and placed in spirits 

 is the very best mode, taking care, however, not to 

 injure the gills or margins of the mantle.* When 

 the sea bathes the roots of trees, as the Mangroves, 

 which it does in many parts of tropical shores, 

 Littorince, Ostrece, Neritince, and Auriculae, will 

 be found on their trunks, and among the branches 

 and roots that are out of the water. Bubbles of 

 air will shew where shells are hid in the mud or 

 sand, as will little hillocks, grooves, holes, and ver- 

 micular-formed heaps of excrement. The bur- 

 rowers in the sand must be turned out promptly 

 by a digging implement of some sort, taking care 

 not to crush the valves by the pressure of the soil 

 around them. The Pholades, and other bivalves 

 that live in calcareous rocks, may be detected by the 



* Chitons placed in salt-water on a piece of slate will adhere 

 naturally, and may then be removed, and their backs held to the 

 fire, when they will dry nicely in situ. 



