[ 485 ] 

 XIII, On the Mechanism of the Odontophore in certain Mollusca. By Patrick Geddes. 



(From the Biological Laboratory of the Eoyal School of Mines.) 



Eeceived November 23rd, 1877. Read February 19th, 1878. 



[Plates LXXX.-LXXXII.] 



After consideration I have resolved to omit describing in full detail the variations 

 of the odontophore in the three types of Mollusca here selected (Loligo, Patella, and 

 Buccinum), and even to omit naming all the muscles figured, since for description the 

 drawings, with their explanation, may suffice, while no nomenclature can be completely 

 rational and permanent till the organ has been exhaustively studied throughout the 

 Odontophora. It is only proposed briefly to attempt an explanation of the principle 

 of the apparatus, incidentally reviewing the leading existing theories of its structure and 

 function. 



Most of the misconceptions which have prevailed on this subject appear to have 

 arisen by commencing with the highly specialised organ of the Whelk, and taking that 

 as a type. A priori it seems better to begin with the Cephalopod, of which the organi- 

 zation in certain other respects appears to have departed much less from the ancestral 

 Molluscan type'. From this point of view the buccal mass of Nautilus should be 

 of extreme interest. 



The reader is doubtless aware that the odontophore in all Cephalophora consists of 

 a toothed radula, placed on a partly muscular and partly cartilaginous support. The 

 single pair of buccal " cartilages " in the Cuttlefish [Loligo) are very slightly developed, 

 mere thin sheets, to which muscles are attached. Their lateral position, sloping 

 upwards and forwards, and their connexion even at the apex by transverse muscular 

 fibres only, are to be noted (figs. 1-9, dtf). Over the sharply crescentiform apical 

 edge formed by this ventral adductor muscle of the cartilages, there fits a stout and 

 equally sharp-edged infraradular sheet (figs. 4 & 5, irs) of muscular fibres with 

 abundant connective tissue, into which is inserted a pair of muscles on the ventral side 

 {vis, fig. 8), while above it is continuous with the longitudinal muscles (fig. 4, edlm, dim) 

 both internal and external to the transverse fibres which connect the cartilages on the 

 dorsal side. Very deep within the inner mass of longitudinal muscles, and as close 

 as possible to the framework, lies the sheath of the radula (figs. 4, 5, 9, rs). The 

 radula itself has a quite sharp and permanent bend (figs. 4 & 5, r), where it passes 

 round the edge of its flexible muscular support, to the sides of which it is also 



' Gegenbaur, ' Gnmdziige der Vergleichenden Anatomie." 



VOL. X. — PAKT XI. No. 1. — Felruary \st, 1879. 3 u 



