VENTRAL PALLIAL COMPLEX. 753 



form but adherent to the posterior declivous surface of the hood and only free at its 

 circumference. This plate is of an aponeurotic texture and a white colour: at both 

 sides it is united to the dorsal fold [italics mine] and below it seems to have an 

 intimate connection with the two side parts of the funnel, and indeed to be a con- 

 tinuation of those parts." The new fact signalised by Van der Hoeven is the relation 

 of the nuchal membrane to the aloe infundibuli into which alone it passes behind and 

 below (PI. LXXVIL fig. 4). 



The umbilical portion of the pallial border is the angle which unites the dorsal 

 and ventro-lateral folds together, and in N. pompilius secretes the callus which conceals 

 the true umbilicus of the shell. 



6. Ventral Pallial Complex. 



In order to render my description of the pallial topography relatively complete it 

 is desirable to devote a special section to an enumeration of the organs which are 

 contained in the spacious mantle-cavity 1 produced by the deep ventro-lateral fold of the 

 mantle. The insertion of this fold into the body-wall is not so easily understood as in 

 the case of the dorsal fold as it involves some of the organs, notably the branchiae, 

 osphradia, anus and renal organs, which in other Cephalopods form part of the body 

 proper and are not carried up into and upon the mantle itself. 



The various organs, lines and regions which compose the ventral pallial complex 

 are mapped out in the coloured figure on Plate LXXV. which shows their exact normal 

 positions in the fresh condition as seen upon and through the thin pallial wall. Such 

 a figure as that referred to is serviceable from the point of view of topographical 

 anatomy on account of the degree of transparency possessed by the living mantle as 

 compared with its opacity in preserved specimens. 



The mantle commences as a free fold behind the renal sacs, so that these structures 

 actually penetrate into the substance of the mantle, and their apertures as well as the 

 viscero-pericardial apertures open upon the inner surface of the mantle. The pallial 

 insertion of the above-named organs and also of the nidamental gland in the female, 

 by all of which Nautilus differs from the Dibranchs, has doubtless been noted by 

 anatomists who have dissected this animal, and has further received special attention from 

 Dr L. E. Griffin 2 , who points out that "there is in the Nautilus pompilius the same 

 arrangement of the parts of the pallial complex as in many Gasteropoda." It may be 

 noted here that the particular Gasteropoda to which Nautilus, in common with other 

 Cephalopoda, is specially comparable, are the Zygobranchiate Prosobranchiata which 

 include Haliotis and Pleurotomaria 3 . 



1 Branchial cavity of Vrolik, sub-pallial chamber of Lankester. 



2 Griffin, L. E., "Notes on the Anatomy of Nautilus pompilius.'" Zool. Bull. (Boston), Vol. I., 1897. 

 Section headed "The Pallial Complex" on p. 153. 



3 For Haliotis see Wegmann, H., " Contributions a l'histoire naturelle des Haliotides." Arch. zool. exper. 

 (2) ii., 1884, pp. 289—379, Pis. xv.— xix. For Pleurotomaria the work of the lamented Martin F. Woodward 

 should be consulted, " The Anatomy of Pleurotomaria beyrichii Hilg." Quart. J. Micr. Be., Vol. 44, March 1901, 

 pp. 215-268. 



