20 GENERAL HISTORY OF 



by the cuticle be admitted, the cells of plants approximate very 

 closely to animals. The difRculties, however, are greatest in the 

 Besmidiacea and JDiamomacea, to which the reader is referred to for 

 particulars. 



4. Composition. Tertiary compounds are claimed for the vegetable, 

 but the Chlamidomonas, whose animal nature is undoubted, is only a 

 tertiaiy compoimd. The presence of nitrogen was, sometime since, 

 excluded from the vegetable, but it is now known that several plants 

 contain azote. 



5. Starch. The existence of the organic proximate element, 

 Starch, has been much insisted upon as detennining this question, 

 i:ideed its almost constant presence in plants, renders it a desirable 

 test ; but, in the doubtful animal organism, their minuteness and 

 the nature of their coverings, render it difficult of application ; 

 indeed, in those cases where it is most needed, as the Desmidiece (which 

 see) it too often gives equivalent results. 



6. Hie evolution of Carhonic Acid hj Animals and of Oxygen hj 

 Plants, has been proposed for detennining tliis point, but the Euglena 

 mridis, whose animal nature is admitted exhales oxygen, as do some 

 of the doubtful family BacUlaria and the Yolvox globator, the latter, 

 however, has lately been claimed by the botanist. 



7. Visual Organs. The existence of eyes would prove, beyond doubt, 

 the animal nature of an organism ; but the red points considered as 

 eyes, which exist in many of the Polygastric Infusoria, are, by some 

 naturalists, not admitted as eyes, similar red spots being observed in 

 the spores of Alg?e, are adduced as confirmatory of this position. 



8. Contractihility has been proposed as a test. It applies only to 

 the soft bodied forms, but M. Thuret says it is not peculiar to animals, 

 but partaken also by the zoospores of Algae. 



9. Multiplication hj s2)ontaneous division or fission. This method of 

 increase has been adduced by Elirenberg, as evidence of the animal 

 nature of the Bacillaria and other Infusoria, but, it is admitted, that 

 the fissiparous division of vegetable cells is of a similar nature. 

 (See Section XVI.) 



10. The non-occurrence of development by conjugation, has been 

 latterly insisted ujion as scparatmg animals from plants, but this 

 distinction is now questioned. (See Desmedca, Part III.) 



