30 



HISTOLOGY, 



H 



CHAPTER IV. 



HISTOLOGY, 



ISTOLOGY is the study of cells. In the case of 

 the Protozoa this is the study of the whole organ- 

 ism ; in the Metazoa, of its constituent units. 



Fig. 4.- 



-Amceboid Cells. 

 2 



I. Amoeba. 2. Leucocyte of Frog. 3. Ovum of Hydra. 

 (After Howes.) (After Kleinenburg.) 



Independent cells may occur in several character- 

 istic conditions. The principal are as follows : — 



I. Amceboid. — These are cells resembling Amoeba^ shape- 

 less, and showing movements by pseudopodia. A number 

 of Protozoa show this condition throughout the greater part 

 of their life. In the Metazoa free amoeboid cells occur with 

 great frequency. They are usually termed leucocytes and 

 fulfil important functions, such as ingestion of bacteria. 

 Leucocytes of this nature occur in great numbers in human 

 blood. 



Fig. 5. — Flagellate Cells. 

 I 2 3 



Spermatozoa. 2. Flagellate Protozoa. 



3. Collared Cell of 

 Sponge. 



