AFFINITIES. 



807 



between Nautilus and Dibranchs, and Nautilus is not specially consulted in the matter, 

 and yet I think it is alone a competent witness. 



The similarities between Nautilus and a diotocard Prosobranch (Haliotis, Fissurella, 

 Pleurotomaria), whether of the nature of affinity or of convergence, include the following 

 points. 



System. 



Circulatory. 



Nervous. 



Sensory. 

 Motor. 



Branchial. 



Pallial. 

 Reproductive. 



Digestive. 



TETRABRANCH I ATA. 



Aorta inferior s. pallialis. 

 Aorta superior s. systemica. 

 Intestinal branch of pallial artery. 

 Reno-branchial system. 

 Peristomial haemocoel. 



(Pleuro-pedal collar. 

 Intra-epidermal fibrillar 

 plexus of osphradium. 

 Eye with perforated cornea. 

 [ Cephalopodium. 

 I Siphonopodium. 



j Branchial folia biserial. 

 (Branchial skeleton. 



Nidamental gland. 



Dioecism. 

 ("Pyloric coecum. 

 < Ciliated intestinal epithelium. 

 [Absence of extrabulbar salivary 



Prosobranchiata. 

 Arteria pallialis. 

 Truncus arteriosus communis. 

 Rectal branch of pallial artery. 

 Similar. 

 Cephalic sinus. 

 Pleuro-pedal cords. 

 Same. 



Same. 



Epipodium. 



Platypodium. 



Same. 



Same. 



Hypobranchial gland (Haller, 1894). 



Same. 



Similar. 



Same. 



Same. 



With regard to the relationship of Nautilus to the other Cephalopoda opinions will 

 always differ as to details, but the main issues are clearly defined. In respect that it 

 is a Cephalopod, the external shell of Nautilus is probably primitive as compared with 

 the internal shell of Spirula and the other Dibranchs 1 . 



Upon the primitive characters of the digestive system, the paired liver, structure 

 of pyloric coecum, etc., Haller (1895) may be consulted. Brock tabulated upwards of 

 a dozen different combinations and correlations of oviducts and nidamental glands, and 

 pointed out that the slit-like orifices of the renal sacs of Nautilus are of primitive 

 significance, inasmuch as this kind of renal orifice is again met with in all Oigopsid 

 cuttle-fishes, and in the more primitive forms of the other subdivisions, whereas in the 

 higher Myopsidae and Octopoda a fleshy renal papilla has developed 2 . He thinks that 

 the Octopoda are the most highly specialised Cephalopoda (as illustrated in the structure 

 of the central nervous system, the eye which can be closed by eyelids, the atrophy of 



1 On vestigial shells of Cephalopoda see Appellof, A., " Uber das Vorkommen innerer Sehalen bei den 

 achtarmigen Cephalopoden (Octopoda)." Bergens Mus. Aarbog. 1898, No. 12. 



2 Brock, J., " Studien uber die Verwandtschaftsverhaltnisse der dibranchiaten Cephalopoden." S. B. Soc. 

 Erlangen, 1879, Heft 11, pp. 114—141. Also Morph. Jahrb., vi. 1880, p. 185. 



