Chapter 3 

 Morphology 



PROTOZOA range in size from ultramicroscopic 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 (ju) 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. 94). 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. 

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

 symmetry, in certain Heliozoa, Volvox, etc. 



The fundamental component of the protozoan body is the pro- 

 toplasm which is without exception differentiated into the nucleus 

 and the cytosome. Haeckel's monera are now considered as non- 

 existent, since improved microscopic technique has failed in recent 

 years to reveal any anucleated protozoans. The nucleus and the cyto- 

 some 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 regeneration of the body is accomplished 

 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 cytosome degenerate, which indi- 

 cates their intimate association in carrying on the activities of the 

 body. It appears certain that the nucleus controls the assimilative 

 phase of metabclism which takes place in the cytosome in normal 

 animals, while the cytosome is capable of carrying on the catabolic 



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