256 FUNCTIONS AND INSTINCTS. 



which are in pairs mutually corresponding, a 

 circumstance not discoverable in the bivalves. 



The escallop shells were considered by Linne 

 as belonging to the same genus with the oyster, 

 which he regarded as a kind of rustic tribe 

 belonging to it ; but they not only differ widely 

 in their shells, but also in the animal they con- 

 tain. The mantle of the former is stated to be 

 composed of two large membranes surrounded 

 with long white hairs, and with pedimculated 

 eyes: whence Poli denominated the animal of 

 this shell " Argus ;" but these assuredly are not 

 real eyes, but probably eye-like organs or ten- 

 tacles, useful to the animal, perhaps, as organs of 

 investigation and prehension, but not of vision. 

 Lamarck, who does not, in loco, mention this 

 formation of the animal of the escallop shells, 

 observes that the Spondyls 1 have the margin of the 

 mantle furnished with two rows of tentacular 

 threads, a structure that seems to indicate some 

 investigating office or prehensory function resi- 

 dent in that part, perhaps like the tentacles of 

 the polypes they may seize animalcules. The 

 animal of the oyster has nothing akin to this, a 

 sufficient proof, added to their very different 

 shells, that they belong to different genera. 



The French call these shells pelerines or 

 pilgrims, they are also in catholic countries, 

 especially in Spain and Portugal, called shells of 



1 Spondylus. 



