190 MR J. D. MACDONALD ON THE ANATOMY OF THE GENUS FIROLA. 



would appear to be exerted on the blood entering the sinus-system ; for during the contrac- 

 tion of the muscular fibres of the latter, and the systole of the auricle, diastole of the 

 mantle-chamber is taking place. A great deal has been said about vital expansion in 

 human physiology, but the instance just given is one in which the expansion of one 

 chamber is facilitated by the contraction of another, having no internal communication 

 with it ; and this I believe to be the office of the remarkable organ in question, as an 

 appendix to the auricle, which communicates so freely with the sinus-system. 



m. Auricle of the heart, or rather its proper position ; for its limits do not appear to be accu- 

 rately defined. 



n. Ventricle, with its closely interlaced muscular substance. 



0. Principal vessel, 

 p. (Esophagus. 



q. Stomach. 



1. Long nerve-trunk, extending from the pedal ganglion to No. 2. 



2. A small nodule of neurine, which, as I imagine, is chiefly respiratory, though it also sends 



filaments to the great vessel and oesophagus. 



3. A stout commissural-nerve, connecting No. 2 with 



4. The cardiac and visceral ganglion. 



5. A conspicuous nerve, supplying the sphincter and radiating muscular fibres of the mantle 



opening, arising, as in Firoloides, from the ganglion No. 4. 



6. A large commissural-nerve, passing from No. 2 to 



7. A lai-ge saucer-shaped ganglion, lying immediately below the ciliated fossa (t). I can now 



safely say, that a body corresponding to this, though much smaller in Firoloides, is truly 

 nei'vous ; but I cannot hazard any theoiy as to its office, though it is obviously in some 

 way connected with that of the ciliated fossa, — probably with respiration. 



In my former paper, I stated my reasons for believing that the sexes are 

 separate in the Heteropoda, and I am sure that this point will require no further 

 proof, though, as far as the sanction of authority is concerned, the more general 

 conviction even now is, that the sexes are combined. The uncertainty existing 

 on the subject amongst zoologists, cannot be better represented than by the follow- 

 ing quotation, verbatim, of Note 9, p. 264, Dr Burnett's translation of Siebold's 

 " Anatomy of the Invertebrata" : — 



" The penis is double, and at the right side of the base of the visceral sac, 

 with Carinaria and Pterotradiea (Milne-Edwaeds, Ann. d. Sc. Nat., xiii. 1840. 

 p. 195 ; xviii. p. 323, PI. x., fig. 3). Quoy and Gaimard (Voy. de 1' Astrolabe, 

 Mollusq., PI. xxviii. fig. 10 ; or Isis, 1834, Taf iii. fig. 10), have figured a 

 long bifid penis, with Pliyllirrlioe, mnhoiTiensis ; and so, if with the other Hetero- 

 poda, the penis is not retractile, as appears to be the case with Carinaria, accord- 

 ing to Milne-Edwards this species would be a male ; while Phyllirrho'e bucepltahis, 

 figured by Peron (Ann. du Museum, xv., fig. 1 ; or Kosse, De Pteropodum 

 ordine. Diss. fig. 1), apparently without a penis, would be a female, although D'Or- 

 BiGNY (Voy . dans I'Amer. Mer. ; or Isis, 1839, p. 519), regards this genus as 

 hermaphrodite. With Atlanta, there is a simple, pointed penis on the right side 



