AND INHERITANCE IN PEDIASTRUM. 393 



apparently may lead to a change of position by all its neighbors and 

 these mutual adjustments and readjustments continue till it seems 

 that a sort of equilibrium is reached. Smith has figured the changes 

 in position of the cells at successive intervals ('i6). As noted, the 

 cells in the peripheral series apparently get their definitive positions 

 first, while movement is still quite active in the interior of the young 

 colony. I have not been able to determine just when cilia appear in 

 the swarmspores or when and how they disappear, but doubtless 

 the duration of the active movements of the cells is an index of the 

 limits of the ciliated stage. 



To give some hint of the size relations and general appearance 

 of the mother cells and the daughter colonies as they are first formed, 

 I have had reproduced in Figs. 15, 16 and 17 photographs of three 

 stages in the development of a mother cell into a young colony. The 

 difficulties in photographing such stages are very great, as rather 

 long exposures are required and it is not easy to find any consider- 

 able number of cells in the same focal plane. Fig. 15 shows the 

 last two cells of a mother colony in which cleavage is complete and 

 swarming is about to begin. All the other cells are already empty 

 and the walls of some of them show faintly. Two young colonies 

 partly out of focus lie nearby. The irregular grouping of the 

 swarmspores in the mother cell shows nothing of the organization 

 of the future colony. There is no evidence of mosaic or any other 

 type of predetermined form inheritance here. In Fig. 16, from a 

 photograph taken a few minutes later, swarming has begun in one 

 of the two mother cells. The vesicle has escaped and lies partly 

 beneath the remaining mother cell. The swarmspores are in active 

 motion and appear only as a gray cloud. It would, of course, re- 

 quire a very short exposure to catch these moving bodies in sharp 

 focus. This figure is less highly magnified than the preceding one 

 and, in all, seven young colonies and part of an eighth are shown 

 lying near, all of them having come earlier from the same parent 

 colony to which the cell just swarming belongs. The figure is 

 printed more deeply, so that the contents of the remaining mother 

 cell appear black, and parts of the outlines of the adjacent empty 

 cells appear more clearly. The attempt was made to focus on the 



