MOLLUSC A. 217 



In the Annals also (xii, p. 305), is a paper by Owen on 

 the tentacula of the N. Pompilius, in which he maintains his 

 formerly expressed opinion, in opposition to the explanation 

 of those organs by Valenciennes, who considers that the nu- 

 merous tentacula correspond to the acetabula on the arms of 

 the other cephalopocls, and that there are only eight true arms. 



PTEROPODA. An interesting Memoir on the Anatomy, 

 Physiology, and Natural History of the Pteropoda, is 

 given by Souleyet, in the Comptes rendus de 1'Acad. des 

 Sciences de Paris, xvii, p. 662 ; Froriep's Not. xxviii, 

 pp. 81 and 97. 



The naked aud couch iferous Pteropoda are distinguished by the greater 

 and less development of the oral organs aud by other anatomical differences. 

 They are all hermaphrodite ; the penis is separated from the rest of the 

 sexual organs, and is merely an exciting organ. Eyes are probably wanting 

 in all the Pteropoda. The nervous collar presents ganglia only below the 

 oesophagus. The author distinguishes in the nervous collar of the [cephalous] 

 Mollusca three divisions [orders of ganglia] : (1) the superior pair of 

 ganglia, which may be either in contact, or so far apart as to pass 

 under the oesophagus, afford the nerves for the organs of sense ; (2) 

 the inferior pair, which may be either in contact or [sometimes] so far 

 separate as to be placed above the oesophagus, serve for locomotion and 

 common sensation ; (3) besides these, at the inferior part of the nervous 

 ring, there is a variable number of ganglia, connected with each other 

 by commissures, and the nerves arising from which are never perfectly 

 symmetrical, and ramify over the branchise and viscera. The inverted posi- 

 tion in swimming is accounted for by the situation of the bulk of the viscera 

 in the superior part of the body ; and the opinion is expressed that a con- 

 tinual swimming movement does not, as is commonly supposed, really occur, 

 but that the animals can partly float along quietly on the surface, or also 

 affix themselves. As regards their systematic position the author does not 

 consider their separation from the Gasteropoda as natural, he assigns them 

 a place near Sulla, Gasteropteron, and Aphysia. The second part of the 

 work contains the description of the genera and species. 



GASTEROPODA. A. Paasch has published in these Arch, 

 ix, I, p. 71, his careful and instructive researches on the 

 Sexual System and Urinary organs of certain (indigenous) 

 hermaphrodite Snails, such as Paludina vivipara. 



Pulmonata. Clarke (Annals xii, p. 333) enumerates 



