376 GENEBAL HISTORY OF THE INFUSOfilA. 



integument, with its iincini, styles, and setae, in such forms as Coleps and 

 EwploteSj and the covering and appendages of Entomostraca and of some in- 

 ferior Annelida ; and some would note the similarity in movements between 

 Coleps and Dajphnia. 



Through the Vorticellina a relation is established with the Bryozoa or 

 cilio-brachiate Polypes — one, indeed, which some naturalists (Agassiz, for 

 instance) affirm to be so intimate, that the two families should be placed to- 

 gether in the same group. 



Lastly, there is, in the case of many Ciliata, a very close apparent affinity, 

 almost amounting to identity (at least, so far as form is concerned) be- 

 tween them and certain embryonic stages of other animals, — for example, 

 of Planarice and of several of the lowest among the Vermes. It is possible, 

 indeed, that some of the presumed independent Ciliata are nought else but 

 larval conditions ; but unless this can be shown by direct observation of their 

 development and transformation, they must be still retained in their present 

 place. The group rei^resented by Bursaria and Paramecium are, as Agassiz 

 (A. N. H. 1850, vol. vi. p. 156) asserts he has satisfied himself by direct in- 

 vestigation, no other than germs of fresh-water worms, " some of which," he 

 writes, " I have seen hatched from eggs of Planaria laid under my eyes." 

 To this assertion Mr. Girard assents {Proceedings of American Association, 

 1848, p. 402). However, there is one caution to be borne in mind in seeking 

 to establish the unity of certain supposed specific forms and known embryonic 

 phases of any animals — viz. not to confound general resemblance with specific 

 identity. For, notwithstanding the former may be veiy distinct and close, 

 this is not enough (as the history of development of the higher animals 

 teaches us) while there is aught wanting in the image, to render it an exact 

 counterpart of the origiual, identical in kind with it. 



The above ofi'ers a general sketch of the most evident affinities of the 

 Ciliata. By the exercise of the imagination directed simply to external form, 

 these might be greatly multiphed : this, however, would, instead of advancing 

 our knowledge, lead only to misconceptions. 



Classification of the Ciliated Protozoa. — Among the many heteroge- 

 neous groups of beings which have at a previous period been assembled under 

 the name of Infusoria, or other terms tantamount to it, that of the ciliated 

 animalcules has been more or less clearly distinguished from the rest, and 

 has received much attention from the several propounders of schemes of clas- 

 sification. However, as our knowledge of the Cihata, both with respect to 

 the number of known species and to their minute organization, on which 

 alone any correct classification can be based, has been so greatly extended 

 during the last few years, it would be useless to describe the various systems 

 which were suggested when, as we may say, this branch of natural history 

 was in its infancy. 



We shall therefore omit aU notice of any systematic arrangement of the 

 Ciliata prior to that proposed by Ehrenberg. Now, although this arrange- 

 ment is very imperfect and incorrect, and founded, moreover, upon certain 

 views of their organization now generally rejected, yet, as it was the system 

 adopted in previous editions of this work, and mil be generally followed in 

 the present one ; and as, moreover, no other classification can lay claim to 

 such completeness and accuracy as to command its adoption instead, it 

 behoves us to detail its principal features. Besides this distribution of Ciliata, 

 suggested by the great micrographer of Berhn, there are three others it 

 win be necessary to describe in this place, severally proposed by Dujardin, 

 Siebold, and Perty. Of these, however, it will only be necessary to present 

 the outline as given by their respective authors, since the examination of the 



