28 On the present state ofZooloyy. 
whether those microscopic marine shells, which have been hitherto ar- 
ranged with the CephalopodousMollusca,a,udm which class they stand 
as D'Orbigny's order of Foraminifera, whether, after all, they do 
not belong to animals possessed of the very simplest organization, and 
such as brings them into close alliance with some of the lowest forms 
among the Infusoria of Muller. Such at least is the opinion of M. 
Dujardin, whose memoir on the structure of these animals, published 
recently, is deserving of attention. * The same observer has been led 
by his researches to question the accuracy of even the brilliant disco- 
veries of Ehrenberg with respect to the Polygastrica. He is inclin- 
ed to think that the supposed alimentary sacs seen by that naturalist 
are simple vacuities formed spontaneously in the midst of a peculiar 
gelatinous substance f which enters into the composition of these ani- 
mals, and through which the water is imbibed into these vacuities. 
He considers the existence of a mouth and anus as a mere illusion. 
Whether these opinions be right or not, they show that our know- 
ledge of the structure of these groups, which is the only sure guide 
to their classification, is not yet upon a sure footing. And how many 
others are there to which the same remark is applicable ? We might 
speak of the Physalice, by some classed with the Acalepha, by others 
with the Mollusca ; J or of the Diphyce, those anomalous beings 
which we are at a loss whether to consider as simple or compound 
animals. We might allude to the strange discovery, recently announ- 
ced by Mr Thompson, that the genus Comatula is, during its young 
state, a species of Pentacrinus, to shew that even in tribes with whose 
structure we are better acquainted, there is yet much to be learnt as 
regards their history. Or, lastly, we might dwell on those extraor- 
dinary productions, which seem to baffle all our conjectures respecting 
their true nature ; which we know not whether to arrange with 
plants or animals, and which some have even regarded as forming an 
intermediate kingdom between the two. || Who does not see, in these 
instances, and in many others which might equally be brought for- 
ward, an ample and almost untrodden field, in which the acquisition 
of only a few facts may lead to the most important discoveries. 
. * See Ann. des Sci. Nat. 1835, torn, iv, p. 343. 
f To this substance, which is said to be found in all the lower animals inter- 
mixed with the other elements of their structure, M. Dujardin gives the name of 
Sarcode -See Ann. des Sci. Nat. 1835, torn. iv. p. 364. 
f Referred to the Mollusca by Blainville See his Manuel d'Actinologie, 
(1834,) p. 112. 
Edin. New Phil. Journ. No. 40, (April 1836,) p. 295. 
|| See the article ARTHROIDEES in the Diet. Class. d'Histoire Naturelle. 
