280 



during the whole of the resting period. It is not until the 

 spring, when a new vegetative period recommences, that the 

 nuclei come close together, and fuse to form a germinal nucleus. 



At this period the zygote, which is surrounded by a delicate 

 membrane, makes its way through the old cellulose wall, whilst 

 its germinal nucleus transforms itself into a large spindle, of 

 somewhat unusual appearance (Fig. 151 /). This divides into 

 two half-spindles (Fig. 151 J/), which, however, do not enter into 

 the resting condition, but immediately prepare to divide again 



-~ ^ "~ 



Fra. 151. Various germinal stages of Closterium. (After Klebahn, PI XIII Figs 6fa 8 

 9, 11, ft.) 



(Fig. 151 1/7). Thus the germinal nucleus divides into four 

 nuclei, by means of two divisions, the second of which succeeds the 

 first without a pause (Fig. 151 IV). 



Meanwhile the protoplasm of the zygote has divided into two 

 hemispheres (Fig. 151 IF), each of which contains two nuclei, 

 which have been produced by the division of one spindle. The 

 two nuclei soon develop differences in appearance, the one (ac- 

 cording to Klebahn, the -large nucleus) becoming large and vesi- 

 cular, whilst the other (the small nucleus) remains small, and 

 finally quite disappears. The small nucleus becomes much more 

 intensely stained than the large one. It seems to me that the 

 former disintegrates and dissolves, just like the fragments of the 

 chief nucleus and the subsidiary spindles in Infusoria. Before 



