370 REVIEWS — A HISTORY OF INFUSORIA. 



many, and since our knowledge of the phases of existence of a large 

 number is so imperfect, it is really impossible to establish any satis- 

 factory classification. On this account, and also to bring together for 

 convenience sake, a mass of information respecting several collections 

 of beings enumerated among the Anenterous Folyyistrica of Ehren- 

 herg, difficult or impossible to arrange under any other heading, we 

 resort to this artificial division, and in so doing have the example of 

 Perty and other writers." The collection of the observations and 

 opinions of the most celebrated and trustworthy microscopists on these 

 minute organisms is certainly of great value, and it is at least a con- 

 siderable advantage to have doubtful and uncertain forms, most of 

 which must now be considered as transient conditions of some of the 

 lowest vegetables, whilst they are described so as to be recognized, 

 and the materials for their study are brought together, carefully se- 

 parated from beings whose animal character is generally admitted, and 

 which are to be considered as members of the lowest sub-kingdom or 

 branch of the animal kingdom. When we see the number of Ehren- 

 berg's genera, and even families, which are now found to be only suc- 

 cessive transformations of some of the lower Algae in the progress of 

 their development, we cannot but acknowledge and rejoice in the 

 bright light thrown upon so obscure a subject, affording the greatest 

 encouragement to persevering labour and patient research. 



The third section. Protozoa, is equal in extent to the two preceding, 

 and contains a full and careful account of observations and opinions 

 in relation to this great division of minute creatures. They are di- 

 vided into the sub-sections Bhizopoda and Ciliata, which last division 

 corresponds to Infusoria in the limited sense now given to it by manj 

 naturalists. In his general table, the author assigns their place among 

 Rhizopoda to Polycystina, Tlialassicollida, and Spongiada, of which 

 groups — lest his subject matter should be too much extended — he has 

 omitted any further notice. Respecting them, we will only suggest 

 that whilst all that is known of them points out Polycystina as true 

 Rhizopoda, the sponges (For if era or A7norphozoa) appear to consti- 

 tute a division of equal rank with Rhizopoda and Ciliata (Infusoria), 

 whilst there are strong reasons for regarding Thalassicollida as only a 

 sub-division of sponges. 



In this slight indication of the nature of the contents of an exten- 

 tensive and elaborate work, we must avoid minute criticism, ecpecialjy 

 of views which are rather recorded than adopted by the authors. The 



