PHYLUM PROTOZOA 49 



In the Microsporidia, each spore contains a single polar capsule 

 which is observable only after treatment with proper reagents. 



Sarcosporidia occur in the muscles of various mammals. The 

 encysted form reaches a length of several millimeters and finally 

 becomes a mass of sickle-shaped spores in clumps separated from 

 each other by partitions. Detailed structure of the spore is 

 not known. The encysted forms of the genus Sarcocystis within 

 the muscles of mammals have long been known under the name 

 of Miescher's corpuscles, but the complete life cycle is not 

 understood. 



SUBPHYLUM CILIOPHORA (INFUSORIA) 



The subphylum Ciliophora includes all Protozoa which possess 

 cilia at least through part of their active life, and in typical 

 instances the nuclear material has become separated into two 

 specialized bodies, one controlling the generative processes (the 

 micronucleus) and the other directing the general activity of the 

 cell (the macronucleus) . Instead of referring to this condition 

 as binucleate, it is more proper to consider the nucleus as dimor- 

 phic, for the micro- and macronuclei combined perform the 

 functions ordinarily exercised by the single nucleus of metazoan 

 cells and of those Protozoa which have single nuclear bodies. 

 In some degenerate forms (Opalina and Ichthyophthirius) there 

 is no distinction of micro- and macronuclei, for two or more similar 

 nuclei occur. There are two classes within this subphylum: the 

 Ciliata, in which cilia are retained throughout life, and the 

 Suctoria, in which cilia are lost after the young individuals 

 become attached to some object. 



Class Ciliata 



As mentioned earlier in this chapter the ciliates represent a 

 degree of complication of parts (see Frontispiece) not found else- 

 where even in the differentiated metazoan cells. It has been 

 maintained by some that the body of the ciliate with its speciali- 

 zation and differentiation of the nuclei represents a differentiation 

 analogous to the separation of somatic and germ cells in the 

 Metazoa. Though the Mastigophora are commonly cited as the 

 protozoan group through which relationships with the Metazoa 

 are traced, there is considerable evidence that this phylogenetic 

 significance is at least shared by the Cihata. 



