210 BIOLOGY OF THE PROTOZOA 



and others, or in a quiescent but not encysted condition in other 

 species of Euglena (E. spirogyra, Phacus pleuronectes, etc.); or in 

 encysted stages in which division may be binary {Euglena deses, 

 Phacus ovvm, etc.) or multiple as in species which give rise to 

 Palmella forms (E. sociahilis, etc., Fig. 95). 



As there are few details in the structure of a simple flagellate on 

 which to focus attention, descriptions of division processes are 

 practically limited to the history of the nucleus, kinetic elements 

 and the more conspicuous plastids. Here, in the main, are fairly 

 prominent granules of different kinds which divide as granules, and, 

 save for the chromatin elements of the nucleus, without obvious 

 mechanisms (see Chapter I, p. 43). 



In the simpler cases there is little evidence that can be interpreted 

 as reorganization at the time of division, and the little we find is 

 limited to the motile organs. In the more complex forms, however, 

 there is marked evidence of deep-seated changes going on in the 

 cell. 



The earlier accounts of cell division in the simpler flagellates 

 described an equal division of all parts of the body including longi- 

 tudinal division of the flagellum, if there were but one, or equal dis- 

 tribution if there were two. One by one such accounts have been 

 checked up by use of modern technical methods until toda}' there 

 is very little substantial evidence of the actual division of a flagel- 

 lum. The basal body and the blepharoplast usually divide, but 

 the flagellum either passes unchanged to one of the daughter cells 

 as in Crithidia (Fig. 48, p. 97), McCulloch) Trypanosoma, etc. 

 (Fig. 97, p. 212), or is absorbed in the cell as in Scytommias subtilis 

 (Fig. 96, Dobell). In some doubtful cases it may be thrown off. 

 If the old flagellum is retained in uniflagellate forms the second 

 flagellum develops by outgrowth from the basal body or the bleph- 

 aroplast (Fig. 96). If the old flagellum is absorbed, both halves of 

 the divided kinetic element give rise to flagella by outgrowths 

 (Fig. 59, p. 117). Similarly if there are two or more flagella, one 

 or more may be retained by each daughter cell while the other, or 

 full number are regenerated (Fig. 98, p. 212). In some cases, as in 

 Herpetomonas musca-domesticoe, the regeneration of a second 

 flagellum occurs before division of the cell is evident, a circumstance 

 which evidently led Prowazek (1905) to conclude that this organism 

 is normally bi-flagellated (Fig. 138, p. 289). 



Reorganization is indicated to some extent by these cases in which 

 the old flagellum is absorbed. It is also evident in those forms of 

 Chrysoflagellida, Cryptoflagellida and Euglenida which reproduce 

 in the palmella or quiescent ])hases after the exudation of a gela- 

 tinous matrix (see Chapter I), and after loss of the characteristic 

 swimming organs. It is still better indicated by a number of 

 flagellates in which the cytoplasmic kinetic elements, as well as the 



