80 American Fisheries Society. 



this complex through the cytoplasm of the body and, because of 

 their great flexibility, appear generally twisted or crossed during 

 the movements of the organism. The axostyles extend to the tail 

 and pass out of the body as the two posterior flagella (fl. 4) 

 through two elongated grooves (gr.). Two darkly staining 

 masses sometimes occur posterior to the nuclei on each side of the 

 axostyles and may be interpreted as the parabasals of various 

 allied forms of the Hexamitidae (14, 15, pb.)- Their function is 

 not clear. 



Mode of Increase. Binary fission with a longitudinal split- 

 ting occurs abundantly and normally in both adult and juvenile 

 stages (2, 9). The extremely mobile body becomes more nearly 

 oval in outline and considerably enlarged. On the completion- 

 of mitosis — in which the nuclei are doubled — and the duplication 

 of the blepharoplast complex, the two bodies pull away from one 

 another from the anterior end posteriorly, each apparently be- 

 coming full fledged within the space of an hour. 



Multiple fission is a common mode of increase in the encysted 

 organism and the changes thus far observed in this process are 

 suggestive of both a sexual and an asexual cycle in the life his- 

 tory. Encystment is frequent. The adult rounds up, decreases 

 slightly in size, becomes quiet and secretes a cyst wall, which is 

 thin and hyaline. During this process the nuclei increase in 

 number and the flagella are lost (3 and 4). Further multiplica- 

 tion of nuclei follows rapidly (5), the cyst becomes considerably 

 enlarged and finally breaks up into definite nucleated structures, 

 resembling eggs or macrogametes. Structures resembling 

 sperms or microgametes — minute, actively swimming bodies — 

 have also been observed within cyst walls. 



It is certain that the life history is extremely complex as 

 regards the developmental phases of the cysts. From our present 

 knowledge of the organisms in this group of protozoa, it is im- 

 possible to distinguish definitely between cysts producing 

 gametes ; i. e., copulation cysts, and those which may be desig- 

 nated as ordinary multiplication cysts which function in the 

 asexual cycle or schizogamy. With the progress that has been 

 made this season, however, the further interpretation of the life 

 cycle does not present insurmountable obstacles. 



Artificial Culture. Young stages have been secured under 

 conditions of artificial culture and they indicate a free swimming. 



