NATICA. 213 



Adriatica/ endeavoured to explain the action of light 

 and temperature on the colouring-glands of the Mol- 

 lusca ; but, although the development and intensity of 

 colour may be stimulated by the above-mentioned agents, 

 his conjectures contributed nothing to the elucidation of 

 a problem so difficult as this. The observations of Bal- 

 dassini (' Memoria sopra le coiichiglie considerate come 

 parte integrante del corpo dei molluschi ') show that the 

 intensity of colour in a shell depends on the age, food, 

 and health of the mollusk. Gould says that the Natica 

 are very voracious, and play a conspicuous part in de- 

 vouring the dead fish and other animals which are thrown 

 up by the tide. The small circular holes with which 

 bivalve shells are often drilled are also (according to 

 him) the work of these Gastropods, and made by them 

 to gain an entrance to the animal apparently so well 

 secured against such a foe. Their foot is so large as to 

 completely envelope their prey. When moving, they 

 burrow just below the surface of the sand ; and their 

 resting-place is generally indicated by a small heap, re- 

 sembling that made by a mole. The foot is permeated 

 by numerous tubular canals or vessels, which absorb 

 water like a sponge (probably through pores opening 

 inwardly) and thus cause this organ to be enormously 

 distended. Mr. Osier suspected, with scarcely any 

 reason, that Natica and lanthina are insectivorous ; he 

 imagined that the foot of the one and the float of the 

 other might be baits to attract the prey which these 

 mollusks were unable to pursue ! The eyes, when 

 present, are subcutaneous, and have escaped the notice 

 of most naturalists ; those of N. Alderi have been de^ 

 scribed by Mr. Clark. Being always covered, they can 

 be of little, if any, use as organs of vision. The nidus 

 or matrix of the spawn is strap-shaped and convoluted, 



