1883,] NATURAL SCIENCES OP PHILADELPHIA. 223 



Moquin-Tandon ^ ; suffice to say that Stephanoff,^ in his descrip- 

 tion of these organs, made many blunders, and at the same time 

 did not seem to have known of the existence of Moquin-Tandon 's 

 work. 



I. — The Formation of the Radula. 



The radula is formed in the odontophore. This consists of four 

 parts, which can be best understood by a reference to the figures. 

 Fig. 4 a (PI. X) represents a horizontal section through the 

 posterior portion of the odontophore. Fig. 4 b (PL X) is a trans- 

 verse section of the same. Botli figures serve to illustrate the 

 four parts making up the odontophore. 



First, we have to distinguish the tongue-papilla (PI. X, fig. 

 4 ac), which fills up the interior of the odontophore; this is 

 surrounded, as is seen in the drawing, by the radula (r). Ex- 

 ternal to the radula is the epithelium of the radula. If we make 

 a transverse section through the odontophore (fig. 4&), we find 

 that the radula (r) has the form of the letter TJ, and consequently 

 does not entirely surround the papilla, while the epithelium of 

 the radula (s) encircles its external surface. At the open part of 

 the letter TJ, where the radula is wanting, the epithelium passes 

 gradually into the papilla. 



The line x in the transverse section (fig. 4 &, PI. X) represents 

 the position of the horizontal section (fig. 4 a). 



The only part not mentioned now is the fourth and most impor- 

 tant of all. I propose to describe it in Helix aperta^ as the parts 

 in this form jfre larger and more distinct than in Ancylus. 



Fig. 5 (PI. X) represents the posterior part of the odontophore, 

 drawn by a camera lucida. It represents that part of the odon- 

 tophore which is enclosed by the bracket (a) in fig. 4 a. 



In ,the drawing we see at that point where the tongue-papilla 

 coalesces with the epithelium of tbe radula, five large, sharply 

 defined cells (1, S, 3^ 4 and o), which I propose calling the matrix 

 of the radula — thus differing from other writers on the subject, 

 who have not seen these cells, and who call the matrix that part 

 to which I have given the name of tongue-papilla. 



Before I pass to the formation of the radula I will first take up 

 the histology of the separate parts of the odontophore in Helix 

 aperta. 



^ Reclier. anat. physiol. s. I'Ancyle, etc., p. 337. 

 ^ U. d. Gesclilectsorg. u. d. Entwick. von Anc, etc. 



