28 On the present state of Zoology. 



whether those microscopic marine shells, which have been hitherto ar- 

 ranged with the Cephalopodous Mollusca } and in which class they stand 

 as D'Orbigny's order of Forcvminifera, — 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 Potygastrica. 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 j- 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 Pht/salice, by some classed with the Acalepha, by others 

 with the Mollusca ; % 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 

 regai'ds 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. 



\ Referred to the Mollusca by Blainville See his Manuel d'Actinologie, 



(1834,) p. 112. 



§ Edin. New Phil. Journ. No. 40, (April 1836,) p. 295. 



II See the article Arthroidees in the Diet. Class. d'Histoire Naturelle. 



