STUDIES IN THE LIFE-HISTORY OF EUGLENA. 33 1 



(c) Migration of the Nucleus. While the changes described 

 above are taking place, the body of the animal tends to become 

 alternately rounded and extended, during which movement the 

 nucleus passes anteriorly until it comes into contact with the 

 lower border of the reservoir. Here the nuclear membrane and 

 the border of the reservoir present a thickened appearance and 

 because of the presence of the kinetic elements at opposite sides of 

 the nucleus might easily be mistaken for a paradesmose (Fig. 8). 

 Such an interpretation has been given to Euglena agilis by Hall 

 (1923). A careful study of these stages has been made and in no 

 case has a definite line been detected other than would be the 

 natural consequence of the coming together of two surfaces such 

 as the nuclear membrane and the border of the reservoir. 



By the time the nucleus has reached the reservoir, the endosome 

 has elongated, passing from spindle to rod shape, then to dumb- 

 bell shape. In the meantime the chromosomes collect in a more 

 or less haphazard fashion along the middle portion of the endo- 

 some. In the main they assume a radial arrangement as in Fig. 7. 

 In this condition each chromosome^hows a definite longitudinal 

 split. 



(d) The Metaphase. The chromosomes, many of which show a 

 longitudinal split during the prophase, and most of which are in 

 the form of loops, now show a distinct separation along the plane 

 of the longitudinal split. The separation of the split halves 

 produces a complicated figure. Those which appear as loops 

 open out from the apex first, gradually assuming a diamond or 

 double V shape. Those not as loops begin to separate at one end 

 first and gradually form elongated single V shape structures which 

 extend the entire length of the equatorial cylinder. As the 

 splitting proceeds the halves come to lie more nearly parallel to 

 the elongating endosome and produce an apparent equatorial 

 cylinder (Fig. 10). This parallel arrangement of the chromo- 

 somes with their subsequent complete separation in the midline 

 might easily be mistaken for a transverse division. 



The endosome assumes a single bend or curve in its middle 

 region with its convex side toward the posterior part of the body 

 of the animal. This is perhaps caused by the increase in its 

 length beyond the width of the body of the animal, the bend 



