MOLLUSCA.
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In the Annals also (xii, p. 305), is a paper by Owen onthe tentacula of the N. Pompilius, in which he maintains hisformerly expressed opinion, in opposition to the explanationof those organs by Valenciennes, who considers that the nu-merous tentacula correspond to the acetabula on the arms ofthe other cephalopods, and that there are only eight true arms.
Pteropoda. —An interesting Memoir on the Anatomy ,Physiology, and Natural History of the Pteropoda, isgiven by Souleyet , in the Comptes rendus de l’Acad. desSciences de Paris, xvii, p. 662; Froriep’s Not. xxviii,pp. 81 and 97.
The naked and concbiferous Pteropoda are distinguished by the greaterand less development of the oral organs and by other anatomical differences.They are all hermaphrodite; the penis is separated from the rest of thesexual organs, and is merely an exciting organ. Eyes are probably wantingin all the Pteropoda. The nervous collar presents ganglia only below theoesophagus. The author distinguishes in the nervous collar of the [cephalous]Mollusca three divisions [orders of ganglia]: (1) the superior pair ofganglia, which may be either in contact, or so far apart as to passunder the oesophagus, afford the nerves for the organs of sense; (2)the inferior pair, which may be either in contact or [sometimes] so farseparate as to be placed above the oesophagus, serve for locomotion andcommon sensation; (3) besides these, at the inferior part of the nervousring, there is a variable number of ganglia, connected with each otherby commissures, and the nerves arising from which are never perfectlysymmetrical, and ramify over the branchiae and viscera. The inverted posi-tion in swimming is accounted for by the situation of the bulk of the viscerain 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 alsoaffix themselves. As regards their systematic position the author does notconsider their separation from the Gasteropoda as natural, he assigns thema place near Bulla, Gasteropteron, and Aphysia. The second part of thework 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 theSexual System and Urinary organs of certain (indigenous)hermaphrodite Snails, such as Paludina vivipara „