WHITE BLOOD-CORPUSCLES. 



145 



entirely sober conclusion, which regards the Amoeba as the 

 particular one-celled organism which gives us an approxi- 

 mate representation of the ancient one-celled ancestral 

 form common to all many-celled organisms. The naked, 

 simple Amoeba possesses a less differentiated and more 

 primary character than most other cells. To this may be 

 added the circumstance, that similar amoeboid cells can be 

 shown in the full-grown bodies of all many-celled animals. 

 For example, they occur as the so-called white blood-cor- 

 puscles among the red blood-cells (corpuscles) in human 

 blood, and in that of all other Vertebrates. They also occur 

 in many Invertebrate animals ; for instance, in the blood of 

 the Snail; and in 1859 I showed that these colourless blood- 

 corpuscles, like independent Amoebae, can assimilate solid 

 particles, can, therefore, eat (Fig. 15). Lately, it has been 

 found that very many different cells, if they have room, 



FIG. 15. Devouring blood-cells of a Naked Sea-snail (Thetis') very 

 much magnified. In connection with the blood-cells of this snail, I was 

 the first to observe the important fact that " the blood-cells of invertebrate 

 animals are uncovered lumps of protoplasm, and, like the AmcebEe, by 

 means of their peculiar movements can absorb matter," can, therefore, 

 " eat." When at Naples (on the 10th of May, 1859) I had injected the 

 blood-vessels of one of these Snails with pulverized indigo dissolved in 

 water, I was much astonished to find after a few hours that the blood 

 cells themselves were more or less filled with fine particles of indigo. By 

 repeated experimental injections, I was able to watch the absorption of the 

 colouring matter into the blood-cells, which was accomplished exactly as by 

 Amoeba?. (See " Monograph of Eadiolaria," 1862, pp. 104, 105.) 



