36 



elp:mei\ts of biology. 



simple or compound, and have the power of throwing out and retracting 

 temporary prolongations of the body-substance (" pseudopodia "). A 

 mouth generally, if not universally, absent. Ex. Sponges. 



Class C. Infusoria (Infusorian Animalcules). — Protozoa mostly 

 with a mouth and short gullet ; destitute of the power of emitting 

 pseudopodia ; furnished with vibrating hair-like processes (cilia) or con- 

 tractile filaments ; the body composed of three distinct layers. Ex. — 

 Bell-animalcule. 



Sub-Kingdom II. — Ccelenterata. 



Animals whose alimentary canal communicates freely with the general 

 space included within the walls of the body, so that the "body-cavity" 

 comes to communicate with the outer medium through the mouth. 

 Body composed of two fundamental layers or membranes, an outer 

 layer or " ectoderm," and an inner layer or " endoderm." No central 

 organ of the circulation or distinct blood-system ; in most no nervous 

 system. Skin furnished with microscopic stinging organs or "thread- 

 cells." Reproductive organs in all, but multiplication often by non- 

 sexual methods (figs. 5 and 8). 



A B 



Fig 8. — Ccelenterata. A Hydra Tule^nris. the common fresh-water Polj'pe (after 

 Hincks). R Diagrammatic section of a Hydra. 



Class A. Hydrozoa. — Walls of the digestive sac not separated from 



