Volltext: The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea (1)

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- 
branchiata : in the higher division, which 
approaches nearest to the Vertebrate ani¬ 
mals, the branchiae are two in number, 
and the order is called Dibranchiata. 
Syn. Polythalamacés, Blamville; Sipho- 
nifera, D’Orbigny ; minus the Spirulidœ 
and Belemnitidœ. 
The Tetrabranchiate Cephalopods, of 
which the Pearly Nautilus (fig. 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 
(a, a) into nume¬ 
rous chambers 
(b, b), 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 
Fig. 205. 
The Pearly Nautilus, Nautilus Pompilius, 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 
JVT. 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 gTOup of animals M. De Haan has pro¬ 
posed the name of Asiphonoidea ; but M. B’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 Règne 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 Cephalopods 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 tentacles 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¬ 
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 prétendus Céphalopodes 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- 
aliæ, Rotaliæ, Truncatulinæ, Cristellariæ, Melloniæ, 
&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 anew 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 Planariæ or Hydras, or any 
other animals of the Acrite suh-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 
Invertebrata, under the name of Symplectom'eres ; 
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 


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