20 ELEMENTARY BIOLOGY. [CHAP. 



If Amcebce are not to be found, their nature may be 

 understood by the examination of bodies, in many respects 

 very similar to them, which occur in the blood of all verte- 

 brate and most invertebrate animals, and are known as the 

 'colourless corpuscles! They are to be met with in abun- 

 dance in a fresh-drawn drop of human blood. In such a 

 drop, after the red corpuscles have run into rolls, irregular 

 bodies will be seen here and there in the meshes of the 

 rolls. If one of these bodies is carefully watched it will 

 be seen to undergo changes of form of the same character 

 as those exhibited by Amoeba, and these motions become 

 much more active if the drop is kept at the temperature of 

 the body by means of a hot stage. Each corpuscle is, in 

 fact, a mass of protoplasm containing a nucleus, and the 

 protoplasm sends out pseudopodia which are strictly com- 

 parable to those of Amoeba. The colourless corpuscles, 

 however, possess no contractile space. 



The colourless corpuscles of the blood of some of the 

 cold-blooded vertebrates, such as Frogs and Newts, may be 

 kept alive for many weeks in serum properly protected from 

 evaporation ; and if finely divided colouring matter, such 

 as indigo, is supplied to them, either in the body or out of 

 it, they take it into their interior in the same way as true 

 Amoebae would. In the earliest condition of the embryo, 

 the whole body is composed of such nucleated cells as the 

 colourless corpuscles of the blood ; and the colourless cor- 

 puscles must be regarded as simply the progeny of such 

 cells, which have not become metamorphosed, and have 

 retained the characteristics of the lowest and most rudi- 

 mentary forms of animal life. 



The Amceba is an animal, not because of its contractility 

 or power of locomotion, but because it never becomes en- 

 closed within a cellulose sac, and because it is devoid of 



