Chapter 3 

 Morphology 



PROTOZOA range in size from ultramicroscopic to macro- 

 scopic, though they are on the whole minute microscopic 

 animals. The parasitic forms, especially cytozoic parasites, are 

 often extremely small, while free-living protozoans are usually of 

 much larger dimensions. Noctiluca, Foraminifera, Radiolaria, 

 many ciliates such as Stentor, Bursaria, etc., represent larger 

 forms. Colonial protozoans such as Carchesium, Zoothamnium, 

 Ophrydium, etc., are even greater than the solitary forms. Plas- 

 modium, Leishmania, and microsporidian spores may be men- 

 tioned as examples of the smallest forms. The unit of measure- 

 ment employed in protozoology is, as in general microscopy, 1 

 micron (/x) which is equal to 0.001 mm. 



The body forms of Protozoa are even more varied, and fre- 

 quently, because of its extreme plasticity it does not remain 

 constant. From a small simple spheroidal mass up to large highly 

 complex forms, all possible body forms occur. Although the 

 great majority are without symmetry, there are some which pos- 

 sess a definite symmetry. Thus bilateral symmetry is noted in all 

 members of Diplomonadina (p. 272); radial symmetry in Gon- 

 ium, Cyclonexis, etc.; and universal symmetry, in certain Helio- 

 zoa, Volvox, etc. 



The fundamental component of the protozoan body is the pro- 

 toplasm which is without exception difTerentiated into the 

 nucleus and the cytosome. Haeckel's monera are now considered 

 as nonexistent, since improved microscopic technique failed in 

 recent years to reveal any anucleated protozoans. The nucleus 

 and the cytosome are inseparably important to the well-being 

 of a protozoan, as has been shown by numerous investigators 

 since Verworn's pioneer work. In all cases, successful regenera- 

 tion of the body is only accomplished by the nucleus-bearing 

 portions and enucleate parts degenerate soon or later. On the 

 other hand, when the nucleus is taken out of a cell, both the 

 nucleus and cytosome degenerate, which indicate their intimate 

 association in carrying on the activities of the body. It appears 

 certain that the nucleus controls the assimilative phase of metab- 



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