ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 23 



Yet we must not rashly conclude that the two principal groups of 

 decapod dibranchiate cephalopods have diverged from Thjsanoieutliis. 

 The structure of the recent OigopsidsB is too imperfectly known to 

 justify so easy a resolution of their phylogeny. 



Affinities of the Cephalopoda.* — Dr. H. von Ihering, after a review 

 of the opinions held by his predecessors, points out that hitherto the 

 questions of their organization have been settled chiefly, if not 

 altogether, by a reference to the Pteropoda ; he now expresses his 

 belief that the Lamellibranchs, Dentalium and the lowest Arthro- 

 cochlides, stand nearer to the Cephalopoda than do the forms just 

 before mentioned. It is scarcely possible to compare the renal or 

 generative organs of the Pteropoda with those of the Cephalopoda. 

 This point is discussed and illustrated in considerable detail ; and, 

 after it, the question of the relation of the Dibranchiate to the Tetra- 

 branchiate Cephalopoda. 



Here the author advances a proposition which is altogether in 

 opposition to the current views on the subject. This is that we must 

 regard the Tetrabranchiata as being derived from the Dibranchiata, 

 and not the latter from the former. He is of opinion that there is no 

 indication at all of the presence in the Dibranchiate forms of any 

 rudiment of a second pair of gills ; so, again, the arms of the Ncndilns 

 are, as is well known, formed on altogether a different arrangement to 

 those of the Dibranchiata ; they would, indeed, seem to have no direct 

 relation to one another. The unpaired oviduct of the Nautilus affords 

 support to the proposition ; and the fact that in some points Nautilus 

 exhibits characters of a less high degree of differentiation must not be 

 taken as the sole criterion of the genetic affinities of the two groups 

 under discussion. Dr. Ihering regards the Octopoda as presenting 

 us with the best idea of the characters of the organization of the 

 most ancient Cephalopoda ; lowly points are especially exhibited in 

 the arrangement of their nervous system, where the suprapharyngeal 

 ganglion is still united with the cerebral, and not widely separated 

 from it, as it is in the Decapoda. The author's views are here sup- 

 ported by the embryological investigations of Dobretzky, who has 

 observed that in Loligo the ganglia only become separated in the 

 course of development. So, again, Brock's observations on the gene- 

 rative organs show that the Octopoda, as compared with the Deca- 

 poda, still show the least modification ; their oviducts, for example, 

 being constantly double. The same remark will apply to Vigelius's 

 account of the renal system of these two groups. 



Turning to the other line of argument — the palaeontological — the 

 author submits that the Ammonites, and their predecessors, the Gonia- 

 tites, were dibranchiate forms ; the results which have led him to this 

 view have been elsewhere discussed by the author. Here he brings 

 into prominence the fact that microscopical investigation shows that, 

 in structure, that curious organ of the Ammonites, the aptychus, is a 

 partially calcified cartilage, which would correspond to the neck- 

 cartilage of the living Decapoda. This point is entered into very 



* Zeitschr. wiss. Zool., xxxv. (1880) pp. 1-22 (1 fig.). 



