20 ELEMENTAKY BIOLOGY. [ill. 



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 Amcebce, 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 comparable to 

 those of Amcebce. 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 colour- 

 less corpuscles of the blood ; and the colourless corpuscles 

 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 rudimentary forms of 

 animal life. 



The Amoeba is an animal, not because of its contractility 

 or power of locomotion, but because it never becomes inclosed 

 within a cellulose sac, and because it is devoid of the power 

 of manufacturing protein from bodies of a comparatively 

 simple chemical composition. The Amoeba has to obtain 

 its protein ready made, in which respect it resembles all true 



