Abstract
THE EVOLUTION OF DIBRANCHIATE CEPHALOPODS.—Dr. J. Brock, in the last number of Gegenbaur's Morphologisches Jahrbuch (vol. vi. p. 185), gives his reasons for dissenting from von Ihering's conclusions on this subject. He has dissected spirit-preparations of many of the principal genera, and he discusses the evidence derived from the shell, the funnel, the muscular system, the radula, the nervous system, and the vascular excretory and reproductive systems. Three anatomically well-marked phyla or groups of genera are made out, of which the Œgopsidæ are the most ancient, and from this group the other two—the Myopsidæ and the Octopods—are derived. The Œgopsids he further divides into two groups—the Ommastrephidæ and the Loligopsidæ, the comparative antiquity of which cannot yet be determined; they are of great interest because they both show important connections with the two other phyla. The Œgopsid forms are primarily true Belemnites, and later developed into the Sepia type, from which stock also the decapods with simple horny shells sprang independently. The octopods, the most highly differentiated phylum, but with an organisation showing a very early origin, and branching from the main type, afford some evidence of relationship to the type of Loligopsis, although they cannot be regarded as having originated from them. Most probably they had a common origin from the primordial dibranchiate form with ten arms. Dr. Brock relies considerably on the oviduct being double in the Œgopsidæ, and single (by reduction) in Myopsidæ; but unless he can support his theory by more developmental facts it can hardly attain sufficient credit for practical use in classification.
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Biological Notes . Nature 22, 277–278 (1880). https://doi.org/10.1038/022277a0
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DOI: https://doi.org/10.1038/022277a0