42 Mr. L. R. Crawshay on 



know their danger ^Yheu this liorrible parasite has attached 

 itself to tlieir shells, and will do their utmost to dislodge 

 it by making rapid contortions of their shells around them 

 as they crawl, even to the extent of overbalancing them- 

 selves, and while the larva perhaps lies motionless on the 

 shell. It is surprising that at such times the larva retains 

 its hold or escapes injury, but it quickly takes up a position 

 near the orifice and makes a ferocious onslaught with its 

 mandibles, which probably soon overpowers its wretched 

 victim ; I have, however, more than once seen a large 

 H. cantiana throw oft" its assailant and escape. 



When the larva enters the shell it lies inside, against 

 the outer wall, and gradually absorbs the moisture, finally 

 consuming the whole or the greater part of the body of 

 the mollusc. After a period varying from eight to sixteen 

 days the shell is thoroughly cleaned out, preparatory to 

 a succeeding period of inactivity and moulting. The 

 larva may then be heard scraping with its mandibles 

 within the shell, and may be seen making a number of 

 journeys backwards, from the centre of the spire to the 

 oriiice, to eject from the shell the accumulated and unoon- 

 sumed matter. The hairy processes seem to aid the work, 

 as a brush, while the larva shutfles backwards down the 

 shell. As the terminal segment reaches the orifice, the 

 anal claspor grips hold of the edge, and, by an undulating 

 movement of the body, the slimy matter is ejected from 

 the shell. I once found a very large larva thus engaged 

 at 10.80 p.m. (iiaving already been working for perhaps 

 half-an-hour). I then watched it for an hour and a half, 

 while it made nine journeys down to the orifice, mostly 

 at intervals of three to tive minutes, and with generally 

 about twenty to twenty-five of these undulating move- 

 ments at the end of a journey. After this I ceased 

 observing it, but I have found that with varying intervals 

 the work may extend over the greater part of a day. In 

 this way the interior of the shell is at length thoroughly 

 cleaned out and made fit for habitation. Tlie larva, which 

 has become gorged with food almost beyond recognition 

 (the dark scuta appearing as isolated patches on the 

 distended white body), then thrusts itself up, with its 

 head towards the centre of the spire, and prepares for 

 moulting, which takes place about four or five weeks from 

 the time of entering the shell, the skin being then cast 

 towards the orifice, where it sometimes closely stops up 



