108 BULLETIN OF THE 



a result of cell proliferation, and a deep pocket has been formed lined by 

 a layer of cells which are still a part of the inner layer of the mother 

 bud. The outer layer of the latter has also been protruded by the ac- 

 tivity of the inner layer, and its cells go to form the outer layer of the 

 young bud. Still another point is to be observed. The centre of the 

 young bud has moved away from the centre of the neck of the mother 

 bud, and thus the former lies nearer to the margin of the colony than the 

 latter. Figure 17, VII. (Plate III.) shows a still more advanced stage 

 in the development of the bud, in which it is sharply separated from 

 its parent, but its inner and its outer layers are still in direct continuity 

 with the inner and outer layers respectively of the mother. 



I have selected this series from the many which might have been 

 chosen to show the origin of the polypide, because it is an intermediate 

 type between two extremes, and because by it the other cases receive an 

 easy explanation. All cases of budding, however, seem to conform to 

 this general law : the greater the difference in age between the youngest 

 and the next older bud, the greater the distance between the points at 

 which they begin to develop. Thus the typical case of a "double bud " 

 is that in which two buds appear to arise at the same time. They origi- 

 nate, as Nitsche observed, from a common mass of cells. A case of two 

 buds, one only slightly younger than the other, is seen in Figure 5. By 

 comparing with Figure 3, in which the older polypide is older than VIL, 

 Figure 5, the difference between the younger buds will be apparent. On 

 the other hand, Figure 4 illustrates a comparatively late formation of 

 the younger bud. The older bud had attained a stage corresponding to 

 Figure 18 (Plate III.), but the younger bud is not older than that seen in 

 Figure 22, II. Just as in the latter case the two layers of the older bud 

 went respectively into those of the younger, so in the present case a 

 direct continuity can be traced between the cells of the inner and outer 

 layers respectively of the younger and older buds. The evidence that 

 the cells composing the inner layer of the young bud have not arisen di- 

 rectly from the ectoderm is derived not only from the continuity of both 

 cell layers of the two buds, but from the presence of the apparently un- 

 modified ectodermic cells lying above the inner layer of the young bud, 

 and sharply marked off from it. Figure 6 shows a later stage of this 

 same type, in which the layers of the young bud are seen well formed, but 

 still very sharply separated from the overlying ectodermal cells. These 

 series afford an interpretation of the extreme type of budding shown in 

 Figure 2, which is not uncommon. The mother polypide has reached a 

 stage corresponding to Figure 18, Plate III. To the left of the neck of 



