98 DIGESTIVE ORGANS. 



plicity of form, etc., of the radiila. In their systematic labors 

 Troschel and Gray raised the radula to the rank of a character 

 of the first importance, in the molluscan, especially the gastropod 

 system, and they accordingly made many changes, rearrange- 

 ments, and improvements. 



To be sure, the tongue and its delicate teeth have been long 

 since known, but they occupied only a subordinate place in the 

 minds of systematists. With Lebert we might agree that 

 Aristotle meant the teeth upon the radula {Hist. Animn. vi, 4.) 

 " habent qusedam os et dentes, ut Limax, acutos et minutos," 

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

 account of them for the first time in Swammerdam upon Palu- 

 dina, 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. " La 

 machoire inferieure," writes Adanson {Hist. Nat. du Seneg., p. 

 11) in a Bulimus, his B. Kambeul, " ne consiste que dans le 

 palals inferieur de la bouche, qu'est tapise d'une membrane 

 coriace, mais extremement mince, blanche et transparente, sur 

 laquelle sont distribues longitudinalement sur deux cens rangs 

 environ vingt mille dents semblables a autant de crochets courbes 

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

 an toucher, on ne les distingue parfaitement qu'au microscope." 



Poll was one of the first to figure the radula? of cephalopods, 

 gastropods and Chiton ; then Savigny in his Zoology of the 

 Description de I'Egypte. Cuvier in his Memoires correctly 

 described the radulte of a number of mollusks, but attached 

 little systematic value to the part. On the other hand, Quoy and 

 Gaimard, and Souleyet in the works describing the collections of 

 their voyages, figured many radulse, but they were not brought 

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

 mode of feeding of mollusks, attention was again more especially'' 

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

 ticularly with reference to their microscopic characters. As 

 already observed, the extensive observations of Loven and 

 Troschel are the most comprehensive in their treatment of the 

 svibject 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 

 partially based upon modifications of the odontophore. 



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

 apparatus for filing off or rasping food and drawing it into the 

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

 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 



