Chapter 3 

 Morphology 



PROTOZOA range in size from submicroscopic to macroscopic, 

 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 dimen- 

 sions. Noctiluca, Foraminifera, Radiolaria, many ciliates such as 

 Stentor, Bursaria, etc., represent larger forms. Colonial proto- 

 zoans such as Carchesium, Zoothamnium, Ophrj^dium, etc., are even 

 greater than the solitary forms. On the other hand, Plasmodium, 

 Leishmania, and microsporidian spores may be mentioned as exam- 

 ples of the smallest forms. The unit of measurement employed in 

 protozoology is, as in general microscopy, 1 micron (n) which is 

 equal to 0.001 mm. 



The body form of Protozoa is even more varied, and because of 

 its extreme plasticity it frequently does not remain constant. Fur- 

 thermore the form and size of a given species may vary according to 

 the kind and amount of food as is discussed elsewhere (p. 109). 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 possess a definite symmetry. Thus 

 bilateral symmetry is noted in all members of Diplomonadina (p. 

 392); radial symmetry in Gonium, Cyclonexis, etc.; and universal 

 symmetry, in certain Heliozoa, Vol vox, etc. 



The fundamental component of the protozoan body is the pro- 

 toplasm which is without exception differentiated into the nucleus 

 and the cytoplasm. Haeckel's (1868, 1870) monera are now considered 

 as nonexistent, since improved microscopic technique has failed in re- 

 cent years to reveal any anucleated protozoans. The nucleus and the 

 cytoplasm are inseparably important to the well-being of a proto- 

 zoan, as has been shown by numerous investigators since Verworn's 

 pioneer work. In all cases, successful regeneration of the body is ac- 

 complished only by the nucleus-bearing portions and enucleate parts 

 degenerate sooner or later. On the other hand, when the nucleus is 

 taken out of a protozoan, both the nucleus and cytoplasm degener- 

 ate, which indicates their intimate association in carrying on the 

 activities of the body. It appears certain that the nucleus controls 

 the assimilative phase of metabolism which takes place in the cyto- 

 plasm in normal animals, while the cytoplasm is capable of carrying 

 on the catabolic phase of the metabolism. Aside from the importance 



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