498 KECOKD OF SCIENCE FOR 1886. 



into the posterior basal lobes of the cerebral gaugliou." The arm nerves 

 and brachial gaugliou therefore owe their origiu, " uot to the pedal but to 

 the cerebral gaugliou," aud von Ihering's suggestion that " the brachial 

 was really a separate portion of the cerebral gaugliou," is thus cor- 

 roborated. 



The comparison is especially interesting between the structure of 

 Naiitilns aud Sepia on the one hand aud Dentalium ou the other. The 

 body of Dentalium is so oriented that " of the two mantle apertures, the 

 larger, through which the foot projects, is turned forward aud down- 

 ward, while the narrower lies at the apical pole of the body. The mantle 

 cavity occurs at the posterior side of the body." In connection with 

 the superior mantle aperture in Dentalium, considerable space is devoted 

 to the discussion of the origin and development of the mantle cavity 

 and cleft. Finally, it is contended that the arms of cephalopods are 

 homologous with and derived from the cirri of the scaphopod or deuta- 

 lioid gasteropods, and special comparison is made with the tentacles of 

 Nautilus, each tentacle of the nautilus being regarded as homologous 

 with an arm. of a dibranchiate cephalopod. These conclusions will 

 doubtless be dissented from by not a few morphologists. (Arbeit. zooL 

 Inst. Univ. Wien, vii, pp. 61-82; J. E. M. S. (2), vi, pp. 950, 951.) 



Living cephalopods. — The recent cephalopods have been investigated 

 by Mr. William Hoyle in connection with the specimens obtained by the 

 Challenger expedition, and a monograph of those acquired by the great 

 expedition, as well as " a catalogue of recent cephalopoda," has been 

 published. 



Mr. Hoyle admits, in his catalogue, " three hundred and eighty-eight 

 species, which are disposed in sixty-eight genera, aud these into four- 

 teen families." Of these species at least sixty to seventy " have 

 been inadequately characterized, so that it is unlikely that they could 

 be recognized from the published descriptions, aud the same is true of 

 several of the genera ; hence it may be said in round numbers that we 

 are acquainted with the fifty or sixty recent genera, containing three 

 hundred species. It is worthy of remark that twenty-nine, or half the 

 genera, contain only one species each, while nearly oue-half the sjiecies 

 one hundred and seventy, belong to the three genera Octopus, Sepia, 

 and Loligoy 



The species have been considered by Hoyle with reference to their 

 distribution and have been referred to three primary groups: (1) the 

 pelagic ; (2) the abyssal; and (3) the littoral. Those of the first two cat- 

 egories have been further associated together as "oceanic" species, and 

 have been distributed in three groups " corresponding to the Atlantic, 

 Pacific, and Indian (including the Southern) Oceans, rather from con- 

 venience than from a belief that such a division is natural, although 

 the great majority are confined to one area. The chief factor limiting 

 their spread," according to Mr. Hoyle, "is i>robably temperature, though 



