950 SUMMARY OF CURRENT RESEARCHES RELATING TO 



vatcd by the supra-intostinal branch of the commissure, it may be 

 concluded that in Ampullaria and all other Ctcnobranchs the gills 

 arc the homologues of tlio left gill and so-called olfactory organ of 

 the Zeugobranchiata ; this is in opposition to the opinion of most 

 writers, who homologize the large gill of the Ctenobranchs with the 

 right gill of Zeugobranchs, and the false gill with the left. The 

 author concludes that the systematic position of Ampullaria is with 

 the zygoneurous Tamioglossata, and that it stands nearest to the 

 Calyptrasida?. 



Morphology and Relationship of Cephalopods.* — In a critical 

 review Prof. C. Grobben continues his studies on the morphology 

 of Cephalopoda, maintainiug his former view that the primitive 

 form is most nearly represented by Dentalium. 



I. Innervation of arms. — In discussing the nature of the arms, 

 over which there has been so much controversy, Grobben notes the 

 facts which appear to him fatal to the theory which would regard 

 them as modifications of the anterior portion of the foot. Relying 

 on the researches of Dietl and others, he notes especially (1) that 

 the cerebral ganglion is continued downwards round the oesophagus, 

 that a portion of the sub-cesophageal mass apparently belonging to 

 the pedal ganglion really belongs to the cerebral ; and (2) that of the 

 nerve-fibres supplying the arms many undoubtedly terminate in the 

 downward directed portions of the brain, but others may be traced 

 through the anterior and posterior lateral commissure into the pos- 

 terior basal lobes of the cerebral ganglion. These facts suggest that 

 the arm-nerves and brachial ganglion owe their origin not to the 

 pedal but to the cerebral ganglion, and point to Ihering's theory 

 that the brachial was really a separated portion of the cerebral 

 ganglion. 



Resuming the facts established in regard to the central nervous 

 system of Nautilus, Grobben notes Ihering's conclusion that all the 

 tentacle-nerves are cerebral nerves. Grobben refers the tentacles to 

 an original position at the sides of the mouth, as in the cephalocones 

 of Clio. He agrees with Ihering in maintaining that in the Di- 

 branchiata the anterior lateral expansions of the cerebral ganglion of 

 Nautilus have been brought into contact in the inferior middle line 

 by continual shortening of the sub-cerebral commissure. Sections 

 show that the anterior lateral commissure contains exclusively nerves 

 for the arms, while the greater portion of the fibres pass by the 

 posterior oesophageal commissure, which undoubtedly represents the 

 united cerebro-pedal and cerebro-visceral commissures. He there- 

 fore regards the anterior lateral commissure as an anteriorly displaced 

 portion of the posterior. 



II. Development of the arms. — Grobben criticizes Eay Lahkester's 

 conclusions drawn from the development of the arms. As to the 

 Pneumodermon larva where the arms appear on the foot at a distance 

 from the head, the fact is emphasized that the innervation is still 

 from the cerebral ganglion. The cirri of Dentalium cannot corre- 



* Arbeit. Zool. Inst. Univ. Wien (Claus), vii. (1886) pp. 61-82 (4 figs.). 



