INVEBTEBRATA, CRYPTOGAMIAj MICROSCOPY, ETC. 601 



MoUusca. 



Phylogeny of the Dibranchiate Cephalopoda.* — In a contribu- 

 tion to this subject, Dr. Brock points out how little has been done 

 since the contributions of Professor Owen, now some forty years old, 

 in aid of our knowledge of the anatomy of the group ; embryologists 

 have done their best to unravel some of the problems of develoijment, 

 and it is now necessary to make some attemj)t at their comparative 

 anatomy. 



Shell. — It seems to be quite certain that the Octopoda arc derived 

 from shell-bearing forms ; Argonauta has in the young the rudiment 

 of a shell-capsule, and Cirrhoteiithis, which is no true Decapod, has an 

 internal shell. 



Musculature. — The examination of this system is attended with 

 very considerable difficulties ; but when done comparatively it 

 exhibits some interesting relations, as the following table will 

 show : — 



(1.) I. The median retractores capitis are neither fused with one 

 another, nor with the lateral muscles — Enoploteutlus. 

 II. The median retractors begin to be fused with one 

 another — Onycliotcuthis. 

 III. Complete fusion of the median retractors with one 

 another, and partial fusion with the lateral muscles — 

 Ommastrcphes, Sepioleuthis, Loligo. 

 IV. Fusion complete — Scpiola. 

 V. lietractors enclosed in a muscular hepatic capsule, which 

 is widely open posteriorly — Sepia. 

 VI. The capsule completely closed, and the deprcssorcs 

 infundibuli attached to it — Octopoda. 

 (2.) I. A cephalo-cervical articulation developed ; the collaris 

 muscle is inserted into the cervical cartilage — CEgopsida 

 (except Loligopsis), Sepiotcutkis, Loligo, Sepia. 

 11. Articulation lost. The collaris forms a closed ring — 



Sepiola. 

 III. The infundibular articulation rudimentary or absent ; 

 the external layer of the collaris fused with the dorsal 

 portion of the mantle — Octopoda. 

 This table gives evidence of a jirogress from the simjile to the 

 more complex, and of the relations which obtain between some of the 

 Dibranchiata and Spirula and Nautilus ; the latter point is argued 

 out in detail. 



With regard to that interesting structure — the valve of the iu- 

 fundibulum — the author points out that it is clear that its loss is au 

 indication of the attainment of a liighcr stage ; biit he urges that this 

 loss may have been brought about iudcijcndeutly in the Loligopsida 

 and in the Octopoda, and that it docs not therefore have any weight 

 in fixing their respective affinities. 



Tlie central nervous system of the Dibranchiata appears to be 

 eminently formed on one type ; in all CT^gopsida the ganglion 



- 'Muri'Lul. Jahibucb,' vi. (ISSO) p. ll>5. 



