INVERTEBRATE ANIMALS. 



SUB-KINGDOM I. PEOTOZOA. 



CHAl'TEli I. 



]. Gexeral Characters of the Protozoa. 2. Classificatiox. 

 3. Gregarinida. 



The sub-kingdom Protozoa (Gr. proton, first ; and zoiin, an animal), 

 as the name implies, is tlie lowest division of the animal kingdom, 

 and its limits are tlierefore necessarily' not 3'et strictly defined. The 

 Protozoa comprise an enormous number of animals, which are mostly 

 so small as to be invisible to the naked ej'e, and can only be satisfac- 

 torily examined undei' pretty high ]iowers of the miei'oscope. For 

 this reason, and becaxise they are almost imiversally found in water, 

 these creatures, often jiojiularly called "animalcules," are almost un- 

 known to the majority of people. Tlie microscojiical foi-ms of the 

 Protozoa swarm in most stagnant ]ioi.ils, and in all waters charged 

 with organic matter so as to afi'ord them food. Every worker with 

 the njicroscope is familiarly acquainted with them, and they e.\hibit 

 ])hen()mena which in many cases render them objects of the highest 

 interest. From theii' low position in the animal scale, it arises that 

 tlie Protozoa are maiidy chai'acterised by the absence of organs and 

 structures which ficcur in higher beings, and they jwjs.se.ss few po.si- 

 tive characters by which tliej' can be distinguished. 



The Protozoa may be defined as animals, generally of a very mi- 

 mtte size, and compoxed of immodi/ieil or n/n//it/>/ modified protoplasm. 

 Tin' tiipii'id mmiilicrx if tlie i/roii/) ore " iinirrllidar," tlie primitire mass 

 of jii-iitiipliisiii ileeeliipiiHi II '' iiiir/riis" ami tliii.i heeomiiii/ O' " eell." 

 Till' " iiiirli'iis" 'mail, liiiii-i'rir, lie idmnif ; mid it /,< imli/ in the Sponges 



