bbO ME. G. BUSK ON THE CHITINOTJS ORGANS 



may be divided, as regards their presumed function, into the pre- 

 hensile (woodcut, Gr) and the retentive (woodcut, I & H). The 



former, from the strength and conformation of the mandible and 

 the corresponding beak, which is not unfrequently toothed or 

 serrate, as well as from the powerful muscles by which the mandible 

 is moved, are evidently fitted to close down upon living prey of 

 some kind ; whilst the latter, having a more or less membranous 

 or extremely delicate mandible, forming, as it were, when closed 

 the lid of a cup-like cavity or receptacle, seem to be adapted for 

 the purpose of simply retaining passive objects ; and correspond- 

 ing with this less active function, the musculature and chitinous 

 framework of the mandible are very much less developed. 



There are many points connected with these organs deserving 

 of close study, and numerous variations, sometimes of a minute 

 character, though from their constancy no doubt important, which 

 demand close attention in comparing different mandibles. Among 

 these points may be mentioned the size, form, and position of 

 the foramen which exists in all the prehensile avicularia, and the 

 points of insertion of the occlusor muscles, &c. Amongst other 

 minute and apparently unimportant characters of this kind, I may 

 mention one which appears, from its constancy, somewhat curious, 

 and may perhaps prove to be of some classificatory value. 



In many of the species of Cellepora belonging to what I have 

 termed the " holostomatous " section, in all the prehensile avi- 

 cularian mandibles (amongst which are included the oral) a 

 minute slender projection or tongue may be seen rising from 



