PART II. 



CHAPTER VIII. 

 SUB-KINGDOM I.— PROTOZOA. 



The sub-kingdom Protozoa, as the name implies, includes the most 

 lowly organised members of the animal kingdom, and may be de- 

 fined as comprising animals composed of undifferentiated protoplasm, 

 or, at most, of protoplasm so far differentiated as to have developed 

 an outer "watt- and a central "nucleus," the organism in the 

 latter case becoming a " cell." In no case are definite " tissues " de- 

 veloped by the differentiation of a primitive cellular aggregate. There 

 is no proper "body-cavity"; no nervous system; and either no ali- 

 mentary apparatus, or one of a rudimentary nature. 



The Protozoa are small, commonly microscopic animals, for the 

 most part aquatic in their habits. The contractile, jelly-like proto- 

 plasm, or " sarcode," of which the body is composed may be en- 

 tirely naked, or may have the power of secreting hard structures, 

 of horn, lime, or flint. The following table exhibits the chief groups 

 of the Protozoa. 



Class I. Gregarinid.e. — Protozoa in which the body has the form of 

 a simple cell, without any mouth-aperture, and destitute of the power of 

 emitting " pseudopodia." The Gregarines are for the most part internal 

 parasites, and possess no hard structures. 



Class II. — Rhizopoda (Sarcodixa). — Protozoa which are destitute 

 of a mouth, and have the power of emitting extensile and contractile pro- 

 cesses of protoplasm (" pseudopodia "). The sarcode may or may not 

 have the power of secreting hard structures. 



Order i. Monera. — Ex. Protamceba. 

 Order 2. Amccbea. — Ex. Amoeba. 

 Order 3. Foraminifcra. — Ex. Globigerina. 

 Order 4. Radio laria. — Ex. Haliomma. 

 Order 5. Heliozoa. — Ex. Actinophrys. 



