AND CLASSIFICATION OF THE HETEKOPODA. 7 



As far as I have yet discovered with any certainty, the visceral ganglia are two 

 in number — viz., 1st, A minute nodule of neurine (Plate I. fig. 4, d), joined by the 

 commissural nerve above mentioned, and situate at the angle between the origin 

 of the visceral artery and the continuation of the main trunk; and, 2dly, a much 

 larger oblong subquadrilateral ganglion (Plate I. fig. 4, e), lying on the right wall of 

 the intestine near its origin. From the superior angles of the latter body distinct 

 branches take their rise ; one in particular joining the former ganglion, while others 

 are distributed to the heart and everted mantle with its sphincter-like opening. 

 The digestiv^e and internal generative organs are supplied with nerves from the 

 inferior angles of the same nervous centre. 



Digestive System. —The proboscis of Firoloides is susceptible of retraction and 

 protrusion to a considerable extent, in which movements the fore-part of the 

 common muscular sheath, and even the oesophagus itself, plays an important 

 part (Plate I. fig. 2, g). 



The oral orifice (Platel.fig.2, a) is terminal, rounded, and unfurnished with labial 

 plates or mandibles of any kind. The buccal mass (Plate I. fig. 2, d) is small, and 

 placed nearthe extremity of the muzzle, as above-mentioned. The lingual cartilages, 

 in which the cell structure is beautifully marked, are oval in shape, wrapped to- 

 gether by ligaments, and supplied with muscles to effect their varied movements. 



The tongue-sac is scarcely longer than the cartilages, terminating posteriorly 

 in a rounded extremity, and the dental area exhibits a remarkable increase in its 

 breadth from before backwards. The rachidian plates (Plate I. fig. 5, o) being con- 

 cave both in front and behind, are broadly (H) shaped, and bear a large central 

 tooth, with a little comb of denticles on either side . The first or inner pleural plates 

 (Plate I. fig. 5, 1) are destitute of a small inner tooth near the base of the large 

 cusp, and the uncini very nearly equal the breadth of the pleurae, as given in 

 Plate I. fig. 5. 



An elongated and somewhat flattened salivary gland (Plate I. fig. 2, c) lies 

 along the lingual cartilage on either side, and communicates with the mouth by 

 a very short duct. 



The oesophagus, proceeding from the upper and fore-part of the buccal mass, 

 takes a course directly backwards, in close relationship with the buccal artery 

 and nerves, and having reached the visceral nucleus, the canal exhibits a slight 

 gastric enlargement, which receives the biliary ducts inferiorly from the supero- 

 posterior wall of the stomach ; a short intestine passes upwards and backwards 

 between the heart and the abdominal viscera, and terminates in the anus (Plate I. 

 fig. 4, o) on a little prominence above the latter organs, and below and between 

 two small anal lobes or leaflets (Plate I. fig. 4, p). 



The lining membrane of the stomach and intestine is richly ciliated, but the 

 cilia increase both in size and activity as they approach the vent, around which 

 they may be very distinctly observed. The apparently undulatory movement 



