42 REVIEWS. 



the plant has tissues composed of cellulose, or of binary and ternary com- 

 pounds. 



With these may be compared the subjoined parallel considerations : — 

 1 . The Corynidae, Sertularidae, and many other undoubted animals, 

 are fixed to foreign supports, that is, rooted, just as Laminaria and most 

 sea- weeds are rooted. The common Duckweed is not rooted : is it, there- 

 fore, not a plant (?) 



The Tceniadae and Acanthocephala have neither mouth nor stomach. 

 The males of Rotifers are in a similar predicament. Are such organisms 

 plants ? 



3. Plants exhale oxygen, it is true; but they also, like animals, ex- 

 hale carbonic acid. The experiments of Saussure are conclusive upon 

 this point. 



4. Every plant contains nitrogen in its tissues. According to the 

 analysis of Chevandier, wood yields from 0*67 to 1*52 of nitrogen. And 

 in an approved Manual of Chemistry we read, 



" That certain of the azotised principles of plants, which often abound, and are never 

 altogether absent, have a chemical composition and assemblage of properties which as- 

 similate them in the closest manner, and, it is believed, even identify them, with the 

 azotised principles of the animal body : vegetable albumen, fibrin, and casein, are scarcely 

 to be distinguished from the bodies of the same name extracted from blood and milk." 



And in the tests of Ascidians, a deposit of cellulose takes place, pre- 

 cisely after the manner of its formation in the tissues of plants. 



So much, then, for Professor Owen's distinctions between the animal 

 and vegetable kingdoms. They prepare us to understand his implied 

 definition of the organisms included in his new kingdom of Protozoa. 

 These " manifest the common organic characters," or, in other words, 

 perform the vital act of nutrition, " but without the distinct super-addi- 

 tions of plants and animals." It follows, therefore, as a necessary infer- 

 ence from the quotations above made, that the anomalous beings in ques- 

 tion neither move nor are rooted, but remain in some peculiar physical 

 condition yet to be explained; that they do not receive nutritive matter 

 by a mouth, and, at the same time, differ from organisms which have 

 neither mouth nor stomach ; that they neither inhale nor exhale oxygen; 

 and that neither binary, ternary, nor quaternary compounds enter into 

 the composition of their tissues. Such, according to Professor Owen, 

 are the distinctive characteristics of the organic kingdom, Protozoa. 



We conclude, however, that a line of demarcation exists between 

 the animal and vegetable kingdoms, and that the Protozoa, rightly .so 

 called, have their place on the animal side of the line. The unpre- 

 judiced reader of Lieberkiihn's careful memoirs can no longer remain 

 in doubt as to the animal nature of the Sponges. And it is for him who 

 disputes the vegetability of the Diatoms and Desmids to set aside the 

 long series of observations inaugurated by the positive discoveries of 

 Thwaites and Ralfs. The difficulty of expressing, by definition, the 

 distinctions between plants and animals rests, be it remembered, more 



