THE ORIGIN OF THE ANIMAL KINGDOM. 63 



unit. It was therefore extremely significant to find 

 that in their embryology all animals and plants alike 



FIG. 3. Types of Protozoa. I Amoeba. 2 Actinospherum. j Paramecium. 

 4 Vorticella dividing. 5 Euglena. 6 Trichomonas. ' 7 Podophyra. 



began life as a single cell, the egg and the germ cell 

 of the plant being always single cells. To find the 

 cell as the unit of life, to find a group of unicellular 



