MORPHOLOGY OF THE TENTACLES OF NAUTILUS. 801 



are not furnished with suckers but with delicate filiform tentacula, but the fact is that 

 there is a median row of suckers as in Eledone, though the suckers are reduced, and 

 alternating with them are 26 pairs of cirri on each arm'. 



When we come to consider the broader interpretation of the arms of Cephalopoda 

 from a pan-molluscan standpoint we are again confronted with two rival theories which 

 may be defined as follows :^ 



1. Pedal Theory of Huxley' (1853), according to which the arms of Cephalopoda are 

 derivatives of the primitive moUuscan foot. 



2. Cephalic Theory of Leuckart (1848) and von Jhering (1877), according to which 

 they are special appendages and derivatives of the primitive head. 



The most complete exposition of the Pedal Theory is contained in the memoir by 

 Pelseneer^, while the Cephalic Theory has been strongly advocated by Grobben*, and more 

 recently by Kerr'. 



Huxley, as is well known, regarded the arms of Cephalopoda as representing the 

 protopodium and the funnel the epipodium ^ " The formation of an abdomen," he said, 

 " with a peculiar development of the margins of the foot into elongated processes, and 

 with cohesion of the posterior epipodial lobes, gives us the Cephalopodan subtj-pe." 

 From this quotation it is clear that Huxley considered the arms as marginal appendages, 

 which is in itself an important conclusion. His reason for identifying them with the 

 protopodium may possibly be looked for in the bionomical fact that Octopus, for example, 

 actually does crawl about fi-om place to place by means of its arms, although it can 

 s\vim vigorously on occasion. The identification of the funnel with the epipodium may 

 be due to the fact of the cleft funnel of Nautilus, the flaps of which may be likened 

 to pteropodial lobes. 



Grenacher {Zeitschr. wiss. Zool., Bd. 24, 1874) homologised the aims with the velum 

 of Gastropod embryos, but adopted Huxley's interpretation of the funnel on account of 

 the development of the latter from paired primordia. 



The special reasons for the view that the funnel is an epipodial derivative are there- 

 fore based upon facts of bionomics, comparative anatomy, and embryolog)', but I believe 

 that these are facts which mask the truth in this particular case. The epipodium as 

 the name implies lies dorsad of the protopodium, while the siphonopodium of Cephalopods 

 is ventral in position, and although great allowances may be made for changes of topo- 



1 Eschricht, Cirroteuthis mUlleri; Nona Acta Ac. German, t. 18, 1836, p. 627, tabb. 46 — 48. "Octopus 

 snctoriis minimis unam seriem in quovis brachio formantibus ; braohiis cirratis et cum merabrana natatoria 

 usque ad apicem fere connatis." 



^ Huxley, T. H., " On the morphology of the cephalous Mollusca as illustrated by the anatomy of certain 

 Heteropoda and Pteropoda collected duriug the voyage of H.M.S. Rattlesnake in 1846 — 50." Phil. Trans. 

 Vol. 143, 1853, pp. 29—65. 



* Pelseneer, P., " Sur la valeur morphologique des bras des C^phalopodes." Arch. Biol., viii. p. 723, 



18H8; see also Dr Pelseueer's "Report on the Pteropoda." Chall. Rep., Part 60, Vol. xix. 1888. Anatomy 

 (Part in. of Report) Chapter ii. "Are the Pteropoda Cephalopoda?" p. 60. 



■• Grobben, C, " Morphologische Studien iiber Cephalopoden." Arb. Inst. U'ien, v. 1884, see p. 222 



(p. 44 of Separat. Abd.). Also Grobben, C, " Zur Kenntniss der Morphologie und der Verwaudtschaftsverhiiltnisse 

 der Cephalopoden." Arb. Inst. Wien, vii. 1886, pp. 60—82. 



° Kerr, J. G., op. cit. P. Zool. Sac. London, 1895, see p. 678. 



6 Huxley, T. H., op. cit. 1853, PI. v. fig. 5, p. 51. 



