124 REVIEWS. 



But there was wanting some interpreter, some medium, by whom 

 this vast mass of knowledge might be made available to the micro- 

 scopists of Britain. Such a medium science has found in Dr. Pritchard, 

 whose history of the Infusoria is, to some extent, an English re-issue 

 of the classical work of Ehrenberg. 



The fourth edition of Dr. Pritchard' s book, which has just made 

 its appearance, is, however, much more than this. It contains copious 

 statements of the views which modern observers entertain in opposition 

 to Ehrenberg' s doctrines ; and the Infusoria of that writer are by no 

 means regarded as constituting one great natural assemblage. 



If this be so, some one may ask, why has Dr. Pritchard included 

 in a single treatise descriptions of living forms acknowledged to differ thus 

 widely from one another ? The reply is, that all these forms, however 

 dissimilar in structure, agree, with but few exceptions, in their ex- 

 tremely minute size and community of aquatic habit. Hence they are 

 liable to be studied in succession by the same investigator, who na- 

 turally desires to find as much information as possible concerning them 

 within the compass of one volume. 



Yet we do not coincide with Dr. Pritchard in his proposal to retain 

 the term Infusoria, as a convenient collective designation for^the various 

 groups in question. Would it not be more appropriate to restrict the 

 application of this word to the stomatode Protozoa ? These, with a few 

 other forms, are by Dr. Pritchard distinguished as "Ciliata." But it 

 might be questioned whether all the true Infusoria present conspicuous 

 cilia. Is not the possession of a mouth the only constant feature where- 

 by they may definably be separated from other Protozoa ? 



The several divisions of Dr. Pritchard' s work together form one 

 thick octavo volume of nearly a thousand pages. Its entire contents are 

 arranged under two principal parts : the first being a general, and the 

 second, a systematic history of " Infusoria." 



The first part contains five sections. Section I. treats of the Bacillaria 

 of Ehrenberg, including the Diatoms, Desmids, and a third group sepa- 

 rated from the latter under the name of Pediastrese. In section II. are 

 discussed certain other low vegetable forms, mostly locomotive, and fur- 

 nished with whip-like cilia. These are termed Phytozoa, and corre- 

 spond to the group denominated Flagellata by Cohn, and Volvocineae by 

 Henfrey. To us this employment of the word Phytozoa appears ob- 

 jectionable, conveying, as it does, an erroneous view of the nature of 

 the organisms so entitled. It is, moreover, merely an inversion of the 

 old term Zoophyta, already used in so many different significations. 



The remainder of the first part is devoted solely to animal forms : 

 section III. treating of Protozoa ; section IV. of Rotifera ; and section 

 V. of Tardigrada. 



The section on Protozoa gives a general account of the fresh-water 

 Rhizopods, Gregarinida, Infusoria proper, and Noctilucida. The Ichthy- 

 dina are noticed as a special sub-group, — the author being, we think, 

 justified in his exclusion of these anomalous creatures from the well- 

 marked division of Eotifera. But we are not disposed to agree with his 



