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 1 . 



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 2 (1853), according to which the arms of Cephalopoda are 

 derivatives of the primitive molluscan 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 3 , while the Cephalic Theory has been strongly advocated by Grobben 4 , and more 

 recently by Kerr 5 . 



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

 protopodium and the funnel the epipodium 6 . "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 subtype." 

 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 from place to place by means of its arms, although it can 

 swim 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 arms 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 embryology, 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 Eschrieht, Cirroteuthis mulleri ; Nova Acta Ac. German, t. 18, 1836, p. 627, tabb. 46 — 48. " Octopus 

 suctoriis minimis unam seriem in quovis brachio formantibus ; braehiis cirratis et cum membrana natatoria 

 usque ad apicem fere connatis." 



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

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

 Vol. 143, 1853, pp. 29—65. 



3 Pelseneer, P., " Sur la valeur morphologique des bras des Cephalopodes." Arch. Biol., vni. p. 723, 



1888; see also Dr Pelseneer's "Report on the Pteropoda." Chall. Rep., Part 66, Vol. xrx. 1888. Anatomy 

 (Part in. of Eeport) Chapter n. "Are the Pteropoda Cephalopoda?" p. 60. 



4 Grobben, C, " Morphologische Studien iiber Cephalopoden." Arb. Inst. Wien, v. 1884, see p. 222 



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

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



5 Kerr, J. G., op. cit. P. Zool. Soc. London, 1895, see p. 678. 



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



