DIGESTIVE ORGANS. 29 



' habent qunedam os et denies, ut Limax, acutos et minutos," 

 and not as Loven held, the jaws, but we meet with a better ac- 

 count of them for the first time in Swammerdam upon Paludina, 

 Littorina and Neritina. 



With many other striking observations upon mollusks we 

 meet with the first description of the radula in Adanson, 

 which with the underlying tongue he regards as a lower jaw. 

 u La inachoire inferieure," writes Adanson (Hist. Nat. du Seneg. 

 p. 17) in a Bulimus, his I>. Kambeul, " ne consiste que dans le 

 palais inferieur de hi bouche, qu'est tapise d'une membrane 

 coriace, mais extremement mince, blanche et .transparente, sur 

 laquelle sont distribues lougitudinalement sur deux cens rangs 

 environ vingt mille dents semblables a autant de crochets cour- 

 bes en arriere. Ces crochets sont si petits qu'on a peine a les 

 sentir au toucher, on ne les distingue parfaitenient qu'au micro- 

 scope." 



Poli was one of the first to figure the radulai of Cephalopods, 

 (lasteropods and Chiton, then Savigny in his Zoology of the 

 Description de 1'Egypte. ( 1 uvier in his Memoires correctly de- 

 scribes the radulse of a number of mollnsks, but attached 

 little systematic value to the part. On the other hand Qnoy and 

 (iaimard, and Souleyet in the works describing the collection of 

 their voyages, iigure many radulte. but they were not brought 

 forward with sufficient prominence. In Osier's work on the 

 mode of feeding of mollusks, attention was again more especially 

 directed to the radulae, and Lebert studied the same more par- 

 ticularly with reference to their microscopic characters. As 

 already observed, the extensive observations of Love'n and 

 Troschel are the most comprehensive in their treatment of the 

 subject of this discussion, though the great work of the latter 

 approaches completion very slowly. We shall hereafter sketch 

 an outline of the classifications which have been wholly or par- 

 tially based upon modifications of the odontophore. 



The tongue, beset with such teeth, is well adapted as an ap- 

 paratus for filing oft' or rasping food and drawing it into the 

 mouth. In mollusks which creep up on the glass sides of n 

 vessel in which they are confined, one can easily observe the 

 mechanism of eating. The tongue with the whole oral mass is 

 pushed forward a little beyond the lips, so that one can see the 



