2 General Morphology of the Protozoa 



of j^rotozoologists are nothing else than the slime-molds of botanists, and 

 the Sarcosporidia, usually considered Sporozoa, are believed by some 

 workers to be molds. 



This situation, which suggests that protozoologists are unable to dis- 

 tinguish animals from plants, is somewhat disconcerting to those who 

 favor consistency in taxonomy. Consequently, various taxonomic reforms 

 have been suggested. The old term. Protista, recalls such an effort by 

 Haeckel, but the Protista were only a heterogeneous collection of micro- 

 organisms with the plant and animal labels obscured. A more positive 

 reform was proposed by Calkins (17) in his decision to eliminate the 

 chlorophyll-bearing flagellates from the Phylum Protozoa. On the face 

 of it, the proposal seemed to be an admission that zoologists had been 

 in error in laying claim to the "Phytomastigophora." However, some of 

 the more interesting colorless phytoflagellates were saved from a botanical 

 fate by arbitrary transfer to the "Zoomastigophora." The resulting mix- 

 tures could not be justified on the basis of sound taxonomic criteria; 

 hence, this innovation has not been generally accepted. The basic classifi- 

 cation of Copeland (33) recognizes a separate Kingdom Protoctista which 

 includes the Protozoa and various groups of algae and fungi. While this 

 suggestion sidesteps the problem of deciding which Protozoa are animals 

 and which are plants, it seems to imply that such Protozoa as the ciliates 

 are more closely related to the red algae and related organisms than they 

 are to the Kingdom Animalia. 



At present, many protozoologists continue to list the phytoflagellates 

 and slime-molds as Protozoa, although they realize that botanists have no 

 objections to placing these groups in the plant kingdom. While the cur- 

 rent practice is a bit confusing taxonomically, there is the advantage that 

 botanists and protozoologists can legitimately maintain equal interest in 

 these groups which apparently represent mergers of the plant and animal 

 kingdoms. 



From the morphological standpoint. Protozoa are often referred to as 

 unicellular animals, in contrast to the multicellular Metazoa. The small 

 size and simple structure of many Protozoa tend to justify this designa- 

 tion. On the other hand, some Protozoa are not so small and are measur- 

 able in millimeters, or even centimeters, instead of microns. Furthermore, 

 the uninucleate condition is far from universal. Many species possess more 

 than one nucleus, and the numbers range from two to many hundreds. 

 Examples are found in each of the major taxonomic groups. Structural 

 complexity often extends beyond a mere increase in number of nuclei. 

 Mycetozoan protoplasm, as noted in Physarum (167), is traversed by chan- 

 nels through which a liquid, containing many granules, flows back and 

 forth in a sort of primitive circulatory system. Multiplicity of flagellar 

 units is associated with multinuclearity in Mastigophora. The result may 

 be many nucleo-flagellar units (karyomastigonts), as in certain Calonym- 



