EVOLUTION OF PROTOZOA 115 



the creeping or semiterrestrial mode of life. From these 

 evolve the forms specialized for the floating pelagic habit, 

 namely, the Foramiiiijera and Radiolaria, protected by an 

 excessive development and elaboration of their skeletal struc- 

 tures.^ Less cautious observers- than Jennings find in the 



Fig. 18. Skeletons of Typical Protozoa. 



B. Siliceous skeleton or shell of a typical radiolarian, Stauraspis siaiiracantha Haeckel, 



170 times the actual size. Owing to their vast numbers, these microscopic, glassy 

 skeletons are an appreciable factor in earth-building. A large part of the island 

 of Barbados is formed of radiolarian ooze. Photographed from a model in the 

 American Museum. 



C. Calcareous skeleton or shell of a typical foraminifer. Globigcn'na bidloidc; d'Orbigny, 



30 times the actual size. As the animal increases in size it forms successively 

 larger shells adjoining the earlier ones until, as shown in the figure, a cluster of 

 shells of increasing size is formed. The name foraminifer refers to the many 

 minute openings, plainly seen in this figure, through which the pseudopodia can 

 pass. Photographed from a model in the American Museum. (Compare Fig. i6, 

 p. 112.) 



Foraminifera the rudiments of the highest functions and the 

 most intelligent behavior of which undifferentiated protoplasm 

 has been found capable. In the Mastigoplwra the body de- 

 velops flagellate organs of locomotion and food-capture. As 

 an offshoot from the ancestors of these forms arose the Ciliata, 

 the most highly organized unicellular typts of living beings, 



^Op. cit., p. 278. - Heron- Allen, Edward, 1915, p. 270. 



