i 68 COMPARATIVE ANATOMY 



It is not known whether there is any limit to the power of 

 multiplication by longitudinal binary division in Euglenae, but 

 probably there is, for at times the individuals come to rest, 

 absorb or cast off their flagella, and each becomes rounded 

 and surrounds itself with a gelatinous cyst wall of some 

 thickness. Often great numbers of Euglenas may be observed 

 in this encysted condition, and, the cysts of adjacent individuals 

 fusing together, they form a scum on the surface of the water, 

 or at the bottom around stones and other objects. After a 

 period of quiescence the encysted organism divides longitudin- 

 ally, the nucleus passing through the mitotic changes already 

 described. Usually there is only one division, and its products, 

 after developing flagella, escape from the cyst and swim off as 

 young Euglenae. But it not infrequently happens that after 

 the first division each of the daughter products secretes a new 

 cyst for itself within the parent cyst, and rests awhile. Each 

 may then divide, so that four cells are formed within the parent 

 cyst, and these four may develop each one a cyst, and, after a 

 further period of rest, divide again, forming eight. Usually 

 the process does not go further, but the parent cyst and the 

 daughter cysts burst, and the eight young Euglenas are 

 liberated. Occasionally, however, the parent cell has been 

 observed to divide repeatedly without the formation of special 

 daughter cysts, as many as thirty-two young Euglenae being 

 formed and eventually set free. A recent observer has 

 described the formation of numerous flagellated young by the 

 repeated division of an encysted individual, an observation 

 which confirms the description given above of division into 

 thirty-two. 



Encystment, though commonly, is not necessarily followed 

 by division. Euglena viridis not infrequently throws off its 

 flagellum, surrounds itself with a gelatinous cyst wall, and, 

 after a period of rest, develops a new flagellum, and emerges to 

 resume an active existence. 



There is no well-authenticated case of conjugation in 

 Euglenoids. 



Our next type of the Flagellata, Bodo saltans (sometimes 

 misnamed Heteromita rostrata\ or the springing Monad, is one 

 of the organisms commonly found in infusions of animal 

 matter which have been allowed to stand for some months. 



