278 HOW DO STARFISHES OPEN OYSTERS? 



to be seen of a mound formation, since it is no longer necessary, on 

 account of the destruction of the adductor muscle. I give the figure, 

 nevertheless, because in this case the starfish has made use of the 

 bottom of the dish as the point of support, or attachment, for a portion 

 of the arms. The position of these arms is exactly the same as in 

 Fig. 3 : the feet on the parts near their centres (above h) being fixed to 

 the oyster's shell, those on the distal parts (a) to the bottom of the dish. 

 In the figure is seen also very clearly the manner in which the stomach 

 (m) is thrown out, and what a significant position it occupies. That 

 I have not succeeded in this case, as I was able to do with Vcjius, 

 in directly observing the whole process of opening, was due to the 

 fact that the oysters were opened by the starfishes at night. Whether 

 this was accidental or not I cannot say. Venus and Natica were taken 

 and opened at whatever time of the day they were offered. 



^fN*. 



Fig. 6. 



An examination of shells which have been eaten out, also shows that 

 the starfish pulls powerfully upon the shell of an oyster which he is 

 about to devour. The margin of oyster shells, at least at Naples, is 

 always more or less laminated. Now, in oysters which have been eaten 

 out, the laminated margin of the upper shell is always broken away for 

 a greater or less distance, until the deeper and stronger layers are 

 reached. Fig. 6 shows such a shell; on which, however, the injured 

 place was specially conspicuous. I need hardly mention that I care- 

 fully examined the margins of the oysters before giving them to the 

 starfishes. As no other animals were in the dish excepting oysters and 

 starfishes, the effect upon the shells of the oysters which were eaten 

 could only be due to the starfishes. Moreover, I have seen such broken 

 portions of shell directly attached to the suckers on the feet of a star- 

 fish which was resting upon an oyster. Such broken places I have only 

 found on the flat shell, which is clearly due to the curved shell being 

 less laminated, and, therefore, less easily injured. 



