DORIS. 



The species in the first section show varieties of structure that might admit of farther 

 subdivision, but the British forms contained in it are so few, that we think it unnecessary at 

 present to carry the analysis further. 



Cuvier has given a description and figures of the anatomy of Doris in the f Memoires des 

 Mollusques ;' but these, though sufficient for the purpose then contemplated by the great 

 physiologist, do not go much into detail. It seems desirable, therefore, to extend our 

 observations in the present work ; and for that purpose we have, with the assistance of our 

 friend Dr. Embleton, made careful dissections of the various groups of the genus, and shall 

 now give the results of our investigations at some length, as in this instance they relate to 

 the typical member of a family. 



The mouth opens in front between the cloak and foot, and conducts by a short 

 constricted channel (PL 1, fig. 6 <?), which is provided with an outer (c) and an inner lip (d), 

 to the buccal mass. This is a highly developed organ, of an irregular oval form, the walls (g) 

 being composed of numerous strong muscles, some to assist in the motions of the tongue, 

 others to aid in carrying the whole apparatus to and from the oral aperture. 



The buccal organ varies to some extent in our three sections ; in the first (PL 2, fig. 1 a) 

 it is simple and well developed ; in the second (PL 1, fig. 13 #) it is small, and has in addition 

 a large, circular, and beautifully organised muscular gizzard (c) attached to its upper surface, 

 into which this gizzard opens a little in front of the oesophagus. The gizzard is very 

 peculiar, and we believe nothing like it has been hitherto noticed. It is somewhat lentiform, 

 with the walls very thick and firm, smooth in the interior, having the sides externally covered 

 with regular radiating muscular fibres, and a strong muscular belt encircling the margin. 

 This modification is observed in D. bilamellata, D. aspera, and D. depressa. In the third 

 section the buccal apparatus (fig. 12 b) is very large, being apparently an incorporation or 

 blending of the ordinary buccal mass, and the gizzard (c) of section 2. It is anteriorly 

 enlarged and rounded, with the channel (a) of the mouth opening into it on the under surface, 

 and not in front, as in the other two sections (fig. 13 a). 



The tongue (fig. 6 i) consists of a tubular dentigerous membrane, the upper portion of 

 which is partly enclosed within, and partly expanded upon a conical muscular mass (Ji), 

 (the lingual muscles), the base of which occupies the floor of the mouth, the apex pointing 

 forwards, and the expanded dentigerous surface being opposed to the oesophagus. The lower 

 part of the tongue is prolonged into a delicate pouch (fig. 3 m), which projects beyond the 

 posterior and under part of the buccal organ. In this pouch is generated the membrane, 

 which in its turn gives origin to numerous recurved teeth or spines in rows, which, as they 

 are formed, are, together with the membrane, gradually pushed onwards ; and as those before 

 them are worn away or broken, they successively ascend, and eventually reach the upper 

 expanded part of the tube, which is spread out upon the upper surface of the conical mass 

 of lingual muscles. It is this upper part of the tube (figs. 4 and 7 a), expanded like the 

 mouth of a trumpet, that alone performs the office of prehension ; the other, more 

 strictly tubular portion (b), of considerable length in some species, is that in which the 

 teeth are developed, perfected, and retained until brought into connexion with the muscular 

 apparatus. 



In the first section the tongue is broad (fig. 7), and the rows of teeth transverse. In 

 D. tuberculata the rows are forty four in number, each row comprising one hundred and forty 



