MOLLUSCA. . 1 1 



If these facts in the organization of Spirula be compared with the following characters 

 of Dibranchiate Order of Cephalopods ; viz., 



" The gills not exceeding two in number ; but the branchial circulation is aided by two 

 muscular ventricles, situated at the base of each gill in addition to the third systemic ven- 

 tricle ; there is an organ for secreting and expelling an inky fluid. The parietes of the funnel 

 are entire 1 ," — it will afford a striking instance of the power of prediction afforded by the 

 laws of correlation of animal structures, and of the truth of the inference that a Cephalopod 

 "proved to have eight short arms and two long tentacles," 2 must, notwithstanding it 

 possessed a polythalamous shell, have the characteristic organization of the Dibranchiate Order, 

 in contradistinction to that of the Nautilus, the type of the Tetrabranchiate Cephalopods. 



The additional facts derived from the dissection of the specimen obtained by Capt. Sir 

 Edward Belcher, show that the funnel of the Spirula is provided with an apical valve, and 

 with two basal lateral joints ; that the skull is provided with two large cartilaginous acoustic 

 capsules with otolites ; that the. oesophagus, after passing through the cartilaginous skull, 

 rests upon a large salivary gland, and is then continued, preserving its slender diameter, to a 

 small gizzard ; that this is followed by a laminated pancreatic bag, from which the short 

 intestine proceeds and forms, after one slight bend, the rectum ; that the anus is infundibuli- 

 form, and without an appendage ; that the liver consists of two lobes enveloped in a muscular 

 capsule ; and that the cystic ducts are beset with numerous glandular follicles before termi- 

 nating in the pancreatic sac ; that each gill has its branchial heart, and that this heart is 

 provided with an appendage ; that the systemic heart is transversely fusiform, with an 

 anterior process ; and that the branchial compartment of the mantle is devoid of any trace of 

 median septum. By these additional facts we are enabled to test the value of the assumed 

 co-existence of certain modifications of the Dibranchiate structure with the superaddition of 

 two peduncles to the eight ordinary arms, as shown by the figures of the Spirula given by 

 Lamarck and Peron. 



The Octopods, both Octopus proper and Argonauta, have a well-developed septum of the 

 branchial chamber : Cuvier describes it as the " bride anterieure qui lie la bourse a la masse 

 viscerale." The muscles corresponding to this " bride anterieure " also exist in Sepiola ; but 

 in the Cuttles {Sepia) and Calamaries {Loligo), both these muscles and the septum of the 

 branchial chamber are absent as we find them to be in Spirula. The base of the funnel is 

 provided with a large valvular fold on each side in Octopus and Eledone, but has no lateral 

 joints ; it possesses these joints in the Cuttles and Calamaries, but has not the lateral valvular 

 folds. The interior of the funnel is provided with a valve near its apex in the Calamaries 

 and Cuttles, but not in the Octopods. In the characters of the funnel we find the Spirula 



pu faire sortir par un petit orifice situe a gauche de Farms. Les deux parties principales de l'appareil generateur 

 femelle, savoir, d'un cote, a, droite un ovaire considerable et de 1' autre sans doute un organe de la digestion, for- 

 mant a eux deux presque toute la face inferieure de la masse." p. 379. 



1 Art. Cephalopoda, Cyclopaedia of Anatomy, vol. i. p. 519. 2 lb. p. 520. 



