118 BULLETIN OF THE 



polypide ; and this increase in length, occurring between the polypide 

 and bud, carries the two apart. Unfortunately, I am unable to state 

 definitely how this migration of the young bud away from the mother is 

 effected. If the ectoderm increases in length between the two buds by 

 the proliferation of cells already existing in it, that fact ought to be 

 evinced by a distorted condition of the old cell- walls of the highly meta- 

 morphosed cells of the ectoderm. For, since most of the active proto- 

 plasm is at the base of the ectoderm, its area will increase faster than 

 will the area of the surface of the ectoderm ; and the latter will either 

 rupture or stretch, or else the ectoderm will become concave on its 

 outer side. An application of these criteria to sections of the body- wall 

 in the budding region leads to the conclusion that the ectoderm of 

 Cristatella increases here very slightly, if at all, by a proliferation of 

 cells already existing in it. A search for cell division in this region 

 has yielded the same negative results. There can be no doubt that 

 cells are added to the ectoderm from the neck of the polypide. The 

 process takes place, however, after the daughter bud is well established 

 at some distance from the mother bud. The proliferation of these cells 

 ruptures the old cell-walls of the ectoderm, and increases the area of 

 the body-wall. I shall have occasion to speak of this process more 

 fully in treating of the later period to which it belongs. 



There remains, then, the conclusion, that the cells which go to form 

 the inner layer of the young bud are pushed from the neck of the next 

 older bud by a proliferation of cells in the stolon-like mass, without 

 causing an increase in the area of the body-wall itself. Moreover, I 

 have seen cell proliferation in the stolon-like mass. Another series of 

 facts will lead us to this same conclusion. 



Though the body-wall does not increase by cell proliferation between 

 buds, it does so, I believe, at the margin of the colony. This, it is 

 true, cannot be directly observed with ease, since the multiplication of 

 cells, which tends to increase the breadth of the colony, must also occur 

 at the margin, and one cannot be certain what dimension of the colony 

 wall will be augmented by any given case of nuclear division. My 

 belief rests on the following evidence. (1) In the same adult colony 

 the distance of the youngest bud from the margin is not the same 

 in all regions. This is not w 7 hat we should expect if the distance of 

 the youngest polypides from the margin remained unchanged during the 

 growth of the colony. (2) There is a gradual increase in the amount 

 of metamorphosis exhibited by the cells as one passes from the margin 

 towards the middle of the roof. Figure 60 (Plate VI.) shows a rather 



