518 



CEPHALOPODA. 



In the first of these, which is most 

 closely allied to the Gasteropodous Mol- 

 lusks, the branchiae are four in number, 

 and the order is therefore termed Tetra- 

 branchinta : in the higher division, which 

 approaches nearest to the Vertebrate ani- 

 mals, the branchiae are two in number, 

 and the order is called Dibranchiata. 



Order I. TETRABRANCHIATA. 

 Syn. Polythalamaces, Blainville ; Sipho- 

 nifera, D'Orbigny; minus the Spirulidtc 

 and Belemnitida. 



The Tetrabranchiate Cephalopods, of 

 which the Pearly Nautilus (Jig. 205) 

 may be regarded 

 as the type, are 

 provided with a 

 large external uni- 

 valve shell, sym- 

 metrical in form 

 like the body of 

 the animal which 

 it protects, 

 straight, or con- * 

 voluted on a ver- 

 tical plane, and 

 divided by a se- 

 ries of partitions 

 (o, a) into nume- 

 rous chambers 

 (6, 6), of which the 

 last-formed (6') is 



the largest, and alone contains the body of the 

 animal : a dilatable and contractile tube (c, c) 

 is continued from the posterior part of the 



M. D'Orbigny believes to be constructed by mol- 

 luscous animals of a grade of organization which 

 entitles them to rank with the Cephalopodous class. 

 For this group of animals M. De Haan has pro- 

 posed the name of Asiphonoidea ; but M. D'Orbigny, 

 observing that the chambers of their shells com- 

 municate together by means of one or more fora- 

 mina, has substituted the positive term Foraminifera, 

 and they are placed by Cuvier at the end of the 

 Cephalopodous class under that denomination in 

 the last edition of the Regne Animal. 



Strong evidence has, however, been recently ad- 

 duced to prove that these minute shells owe their 

 existence to animals which have no pretensions to 

 rank with the Cephalopods ; but before we give the 

 account of M. Dujardin, who is the author of this 

 view, we shall first quote M. D'Orbigny's own 

 description of the animal of the shells, the struc- 

 ture of which he has so ably studied and so happily 

 demonstrated by means of enlarged models. 



" The Cophalopods of the Foraminiferous Order 

 have a bursiform body, in the posterior part of 

 which the shell is lodged ; the body of the animal 

 sometimes presents a great size compared to that 

 of the head, to which it is occasionally subservient 

 as a means of protection, entirely surrounding it 

 in the anterior folds of the skin. The head is 

 small, scarcely, if at all, distinct from the body, 

 terminated by numerous tentacle* forming many 

 rows around the mouth, which is central. The 

 animal seems to adhere very slightly to the shell ; 

 it rapidly passes into a state of decomposition after 

 death, when the slightest touch is sufficient to 

 detach it from the shell, in which nothing is left 

 but a coloured liquid which fills all its chambers. 

 The food of these animals consists of different species 

 of Polyps." 



M. De Blainville, however, states, in the Ap- 

 pendix to his Manuel de Malacologie, page 649, 

 that the animal of one of the microscopic genera con- 



Fig. 205. 



The Pearly Nautilus, NautiliM Pompilitts, Linn. 



animal through all the partitions and cham- 

 bers of the shell ; but the attachment of 

 the shell to the body is effected by means of 



tained in his order Cellulacea, viz. Miliola, has no 

 relation whatever in its structure to a Cephalopod, 

 or Cryptodibranche. And more recently M. Dujar- 

 din has read a memoir, entitled ' Sur les Symplec- 

 tomeres, ou pretendus Gephalopodes microscopiques,' 

 in which the results of numerous and apparently 

 careful observations on the soft parts of different 

 genera of the animals in question are directly op- 

 posed to those of M. D'Orbigny. 



M. Dujardin carefully studied the Miliolae,Vortici- 

 aliae, Rotaliae, Truncatulinae, Ciistellariae, Melloniae, 

 &c. in the recent and living state ; and found that 

 the shell'was not internal, and that the animal, which 

 is absolutely deprived of organs of locomotion and 

 even of respiration, is composed of a succession of 

 joints or lobes, which go on increasing successively, 

 and enveloping each other. The only period when 

 the soft parts of the animal are visible externally, 

 is when a new joint is produced which has not com- 

 pleted the formation of its chamber. On breaking 

 the shell, the composition of the animal is found 

 to be as simple as in the Planariae or Hydrae, or any 

 other animals of the Acrite sub-kingdom ; and on 

 dissolving the shell by means of a mixture of 

 alcohol and very weak nitric acid, the entire body 

 is obtained, which is formed of a succession of 

 articulations, occupying all the chambers ; and 

 presenting different aspects in different genera, 

 which accord with the peculiarities of the shell. 



From these observations it necessarily follows 

 that the Foraminifera of M. D'Orbigny cannot be 

 arranged with the Cephalopods, or even placed in 

 the Molluscous Series. M. Dujardin, therefore, 



Proposes to consider them as a distinct class of 

 nvertebrata, under the name of Symplectomeres ; 

 and until further and better evidence be adduced 

 to the contrary, we shall regard these minute ani- 

 mals as having only, in the form and structure of 

 their shells, a remote analogical relation to the 

 Cephalopods. 



