STUDIES IN THE LIFE-HISTORY OF EUGLENA. 329 



and varying behavior of other organoids of the cell. This 

 division occurs in the motile state in some species, in a quiescent 

 but not encysted condition in others while in some a true cyst is 

 formed before the organism divides. In the encysted condition 

 the division may be binary or multiple. Some of our observations 

 indicate that some species may divide in the free swimming 

 condition under proper conditions but when the conditions arise 

 which induce encystment, these conditions being either internal 

 or external or both, the divisions may take place in the cyst. 

 The special problems of encystment are now under investigation 

 and will constitue the subject matter for a later paper. In this 

 paper we are concerned with the details of the division process in 

 Euglena agilis. 



Nuclear Division. 



Three principal changes characterize the beginning of nuclear 

 division : 

 (a) changes in the endosome and the budding off of the kinetic 



complex; 



(6) formation of the chromosomes^ 

 (c) migration of the nucleus anteriorly. 



(a) Changes in the Endosome and the Budding off of the Motor 

 Complex. The endosome seems to become more vacuolated than 

 in a typical vegetative stage, increases in size, and at the same 

 time a small knob or bud appears on one side (Fig. 2). The bud 

 usually appears on the side of the endosome toward the anterior 

 portion of the animal but in several instances it has been observed 

 first in other positions becoming turned anteriorly during the 

 migration of the nucleus. The bud increases in size, becomes a 

 spherical or slightly elongated, deeply staining mass and passes 

 through the hyaline area surrounding the endosome, thence 

 through the chromatin of the outer nucleus to the nuclear 

 membrane. In most instances it can be seen definitely connected 

 to the endosome by a rhizoplast (Figs. 3, 4). 



On the nuclear membrane, the mass, now a distinctly spherical 

 body, divides and the daughter bodies separate and pass gradually 

 to opposite sides of the nucleus (Figs. 4, 5, 6). Later the portion 

 of the nuclear membrane which lies between the bodies is drawn 

 into a fairly definite line when viewed in optical section (Fig. 8). 



