HOW DO STAKFISHES OPEN OYSTERS? 273 



separate parts of the foot of Natica, and in a later paper* I added 

 a further contribution to the subject. I was not quite clear at that 

 time as to the significance of the " shell lobe " (Fig. 2, Sch. Lap.) ; 

 that is to say, the portion of the foot which, in Natica joseigliina almost 

 entirely, in N. millepundata and cbrea only partially, under ordinary 

 circumstances, covers the shell. I have now, however, been able to 

 observe with certainty the use to which this portion of the foot is put. 

 If a few Natica be placed in a dish in which there are some Asterias, 

 rendered hungry by fasting, the molluscs immediately begin to creep 

 about, and the starfishes endeavour to overpower them. The tube-feet 

 of the Asterias are unable to fix themselves to the body of the Natica on 

 account of its slimy surface, and there is only left them the uncovered 

 remnant of the shell. (Fig. 2, Sch.) But here also the attachment is 

 prevented, for the moment the Natica comes into contact with a star- 

 fish it pulls the " shell lobe " of the foot with a jerk over the previously 

 uncovered part of the shell, and thus there is no place left to which the 



Fig. 2. 



suckers of the Asterias can fix. I have observed this proceeding a 

 great many times, and it always takes place so promptly that there can 

 be no doubt as to its connection with the means of defence against 

 starfishes. The drawing of the shell lobe over the shell is brought 

 about by the contraction of the transverse, or, rather, annular muscles 

 of the lobe margin, which act like a sphincter. 



In nature, of course, Natica hardly comes in contact with Asterias, 

 but it does come in contact with Astropecten, and it is clear that the 

 tube-feet of that animal, though they are quite pointed at their ends 

 and have no suckers, will slip from the slimy surface of the Natica just 

 in the same way as the tube-feet of Asterias. 



If a Natica in the contracted state be given to an Asterias, the latter 

 fixes its tube-feet upon all parts of the shell of the mollusc, carries it to 

 its mouth, and tries to digest it. If the Natica, however, has lived for 

 some time in the dish and become used to the conditions of confinement, 

 it does not through terror remain closed, but, as a rule, comes out of its 

 shell immediately, and endeavours to free itself from the starfish. A 



• ScHiEMENZ, P., "Wie bohrt Natica die Muschelnau?" Mitth. Zool. Stat. Kcapel. 

 Bd. 10, pp. 153-169. 1891. 



u 2 



