ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 



303 



halves are the last to separate in the metaphases (Fig. i8), and that 

 they lag behind the other daughter chromosomes in their passage 

 to the poles of the spindle (Figs. 19, 20). Even at the late stage 

 shov/n in Fig. 21, the large daughter chromosome moving toward 

 the lower pole of the figure is still a little in the rear of its fellows, 

 which have reached the spindle pole. In this respect the behavior 

 of the large chromosome recalls that of the X-chromosome in the 

 heterotypic divisions of certain insects, and in some cases at least 



... -x 



17 



Figs. 17-21. Stages in nuclear division in the female gametophyte : 

 Fig. 17, a late prophase, the chromosomes showing longitudinal splitting, in a 

 cell of the calyptra; Fig. 18, a metaphase in an involucral cell; Fig. 19, an 

 anaphase in an involucral cell ; Fig. 20, a later anaphase in a young thallus 

 lobe; Fig. 21, a diaster in a cell at the base of a young lobe; x, the large 

 chromosome. X 3800. 



in the homceotypic divisions of these animals as well. It is quite 

 possible, to be sure, that this lagging of the large chromosome of 

 Sphcvrocarpos is merely a result of its proportionately great size. 

 Relatively few division figures have been observed as yet in the 



