GENERAL ORGANIZATION 717 



The Protozoa belonging to this class are amoeboid organisms during 

 the growing or trophic phase of development, while dissemination is 

 effected by means of resistant spores, which are peculiar in being provided 

 with one or more polar capsules. The latter, under certain conditions of 

 stimulation, as, for instance, those of the intestinal fluids, extrude long 

 filaments which are supposed to attach or anchor the spore to the intestinal 

 wall till the enclosed amoeboid body, the actual infective agent, is able to 

 escape from the spore and invade the tissues of the new host. Gluge 

 (1838) was the first observer to see small spores of one of these parasites 

 in fish, but Johannes Miiller (1841) discovered much larger ones in a 

 number of fish, and referred to them as psorosperms, a name which was 

 long used for them and the spores of coccidia and gregarines. The 

 Cnidosporidia are often grouped with the Sporozoa, which Schaudinn 

 (1900) divided into two sub-classes, the Telosporidia and the Neosporidia, 

 the former to include the coccidia and gregarines, and the latter the 

 Myxosporidiida, Microsporidiida, Actinomyxidiida, and Sarcosporidia 

 The Telosporidia, however, have little in common with the Neosporidia. 

 They have definite intracellular stages, reproduction is by schizogony, 

 while the zygotes resulting from a conjugation of gametes become encysted 

 in resistant oocysts, within which they give rise to sporozoites. The 

 Myxosporidiida, Microsporidiida, and Actinomyxidiida, on the other hand, 

 though sometimes intracellular parasites, reproduce mostly by binary 

 fission and not by schizogony, while the zygotes do not become encysted, 

 nor do they give rise to sporozoites. Furthermore, the very characteristic 

 spores possessing polar capsules are produced. Very little is known about 

 the affinities of the Sarcosporidia, but it seems clear from their com- 

 paratively simple spores that they are in no way related to the Cnido- 

 sporidia, which produce the highly complex spores provided with polar 

 capsules. In their development the spores of Cnidosporidia difi'er 

 fundamentally from those of all other Protozoa, the resistant or encysted 

 stages of which are produced by a cell secreting a capsule round itself. 

 Subsequently the entire cell or the products of its division survive. In the 

 case of the Cnidosporidian spore a single cell divides to form several cells, 

 some of which give rise to the polar capsules, others to the spore mem- 

 branes, while one or two alone survive. The production of the spore 

 involves the sacrifice of several cells for protective purposes, while no such 

 sacrifice is associated with spore formation in other Protozoa. This 

 difference led Emery (1909) and Ikeda (1912) to suggest that the Cnido- 

 sporidia are in reality Metazoa. Attention has been again called to this point 

 by Dunkerly (1925), who sees in this dift"erentiation of cells a process by 

 which Metazoa may have evolved from Protozoa. It seems, therefore, 

 best to follow Hartmann (1907), and separate the Myxosporidiida, Micro- 



