346 FUNCTIONS AND INSTINCTS. 



food is similar, are directed by the will of their 

 Creator to affix themselves externally to any sub- 

 merged bodies that come in their way, whether 

 mineral or animal. All they require seems to be 

 something to attach themselves to, on which 

 they can protrude their tentacular gills, and 

 seize their prey. They must contribute largely, 

 as well as the mining Annelidans of this order, 

 to the production of calcareous matter. Mr. 

 Sowerby suspects that their proboscis may be 

 instrumental in forming the shell, but it seems 

 not properly a proboscis, but merely an opercu- 

 lum on a long footstalk, which was requisite that 

 it might be protruded so far as not to interfere 

 with the action of the gills. 



4. The animals included in Mr. Savigny's first 

 Order, the Nereideans bring us very near to the 

 Condylopes. They have a distinct head, jointed 

 organs like antennae, eyes, a proboscis armed 

 with maxillae, and spurious legs*. They have 

 also certain dorsal scales, which M. Savigny 

 calls elytra, and deems analogous to the organs 

 of flight in insects. These animals seem to 

 afford the first example of the conversion of 

 organs of locomotion into others, employed for 

 a different purpose. I do not mean by this, 

 that, in the progress of the animal's growth, one 

 organ is really converted into another, but that 

 analogous organs, in different tribes or genera, are 

 employed for different purposes. Thus, what in 



