SPECIAL MORPHOLOGY AND TAXONOMY OF SPOROZOA 455 



Order 2. Microsporidia, Balbiani. 



Probably because of their minute size the organisms included in 

 this Order are incompletely known and many points of structure 

 and of life history are still unknown or controversial. They are 

 practically all cell parasites which enter the host by way of the 

 digestive tract from which they may spread to all tissues of the 

 body, causing epidemics not only in fish, but economically more 

 important, costly epidemics in silkworms {Nosema hombyces, Naeg.) 

 and honey bees (No.srma apis, Zander). Pseudopodia and amoeboid 

 movement are rarely observed (Nosema marionis, Thel). Inter- 

 mediate hosts are unknown. 



Agamous reproduction is well established through the observa- 

 tions of many investigators. The agametes are small, uninucleate, 

 and usually with indefinite outlines which scarcely delimit them from 

 the host cell protoplasm; they may have one or several nuclei, and 

 multiply actively by simple division resulting frequently in chain 

 formation through successive nuclear divisions and delayed cell 

 division (Fig. 190). As a result of such agamous reproduction all 

 of the tissues of the host may become infected and myriads of tissue 

 cells destroyed. In many species tumor-like masses are formed in 

 which the organisms are surrounded by a membrane derived from 

 the host and are thus encapsulated; in other species such membranes 

 are absent. In the majority of cases spread of the infection in the 

 same host comes to an end with sporulation, but in some species 

 renewed infection is brought about by the action of the digestive 

 fluids on spores formed in the same organism (Kudo). 



Multiple endogenous budding, or fragmentation of the tropho- 

 zoite into numerous binucleate agametes is described for some 

 forms (Debaisieux, 1920) and these, as in Telosporidia, ultimately 

 give rise to the sporulating individuals. The phenomena of sporula- 

 tion differ widely but there is still much uncertainty in the dift'erent 

 accounts at hand. In some cases the trophozoites are said to pro- 

 duce pansporoblasts as in Myxosporidia during the continued vege- 

 tative life of the individual (Polysporea). Such cases included 

 formerly under the name Blastogenea, are regarded as very doubtful 

 by Doflein (1916, p. 1037). In other cases the trophozoite (pansporo- 

 blast?) breaks up into numerous sporulating cells each of which 

 produces one or more s])ores (Oligosporea) and in still other cases, 

 the entire individual forms a single spore without pansporoblast 

 formation (Monosporea) . The absence of pansporoblasts in such 

 cases is regarded as evidence of extreme adaptation on the part of 

 the exclusively cytozoic parasites (Nosema species). 



The spores on the whole are less comjjlex than those of the ]M\'xo- 

 sporidia. They are small and ovoidal or bean-shape and rarely 

 {Telomyxa, Leger and Hesse, 1910) with more than one polar capsule, 



