426 RICHARD EVANS. 



view. In the first place, the peculiar grouping and incompletely 

 divided condition of the cells does not fit in with the view 

 under consideration. In the second place, no cells have been 

 observed in the act of migrating from the flagellated layer in 

 type B. When all these facts have been considered, the 

 balance of evidence seems to be against the view that they 

 liave originated from the flagellated cells by immigration. 



The second possible view of their origin is tliat they have 

 been developed indirectly from the cells with vesicular nuclei, 

 which were first of all transformed into cells with granular 

 nuclei, which, in their turn, divided and subdivided to pro- 

 duce the groups in question. There is only one argument in 

 favour of this view, the fact, namelj'', that the nuclei could 

 be described as being granular, which is of doubtful importance, 

 since the nuclei of the flagellated cells could also be described 

 as being granular. On the other hand, there are several 

 reasons for rejecting this view. In the first place, the cells 

 with vesicular nuclei as well as those with granular nuclei 

 divide by mitosis, but at no time was a karyokinetic figure 

 found in these groups of small nuclei, in spite of the fact that 

 these cells themselves later on divide by mitosis. In the second 

 place, when the cells with granular nuclei divide, the daughter- 

 cells become completely separated from one another, the con- 

 stricted nuclear spindle being often seen as a fine thread con- 

 necting the two cells ; but here a great number of nuclei lie in 

 a mass of cytoplasm, which as yet shows hardly any sign of 

 dividing (figs. 5 a and b, and 9 a and b). In the third place, 

 these nuclei are remarkably uniform in size, which would not 

 have been the case had they originated from those of the cells 

 with granular nuclei. The nuclei of the latter are much 

 larger, and diff'er among themselves in size. This uniformity 

 in size is a most remarkable thing, for in later stages, when 

 these cells become tlie collar-cells, their nuclei are not uniform, 

 since they divide repeatedly, and consequently the size of the 

 nucleus varies. The equality of size alone, apart from any 

 other argument, would incline us towards the opinion that the 

 nuclei of the cell groups in type B have been produced not by 



