MITOSIS AND CELL DIVISION IX EUGLENA. Ill 



division was complete cell cleavage would continue while exposed 

 to this light but would be greatly retarded. The lig-hts in the 

 laboratory, however, seemed to have no effect. 



Acknowledgment. 



Many thanks are due Dr. R. C. Rhodes under whose direction 

 this work was started, and to Dr. R. W. Hegner under whose 

 direction it was completed. 



III. MITOSIS. 



1. The vegetative nucleus (Fig. i) is of the vesicular type, de- 

 scribed for other euglenoids by Tschenzoff (1916), Hall (1923), 

 Baker (1926), and others, and lies mid-way of the longitudinal 

 axis of the cell. It is elipsoidal in shape and is surrounded by a 

 nuclear membrane (Fig. i) which persists throughout mitosis, and 

 which is usually drawn out toward the blepharoplast during vege- 

 tative life. The chromatin is in the form of homogeneous 

 granules arranged in paired rows or strands that lie at random 

 about the endosome which is centrally placed. This body is 

 elongate and varies in appearance in different nuclei. It is en- 

 larged about a vacuole which may occupy any position in its sub- 

 stance (Fig. i, a, b, c~), and which contains a large granule of the 

 same staining capacity as other parts of this structure. A similar 

 granule of practically the same size lies among the chromatin 

 threads in some part of the nucleus which, during the prophase of 

 mitosis, forms the blepharoplasts of the daughter organisms. At 

 this stage it has been called the intranuclear body (Fig. i). The 

 significance of the former granule is not known nor can it be 

 traced through division. It appears, however, as a constant 

 feature of the endosome. 



2. Prophase. With the initiation of division the intranuclear 

 body moves toward the anterior end of the nucleus, divides (Fig. 

 i,a,b,c), and the halves come to lie on the anterior border of the 

 nuclear membrane. The nucleus moves forward (Fig. 2, 3, 4) 

 into contact with the base of the reservoir. The flagellum shortens 

 until it is drawn into the exterior opening of the reservoir (Fig. 

 4). The mass at the bifurcation disappears and the blepharo- 

 plasts move apart so that the axial filaments form an inverted V 



