4 BULLETIN OF THE 



nearly to a straight liue. The point at which the upper and lower 

 curves most nearly approach eacli other is where the separation of two 

 individuals takes place ; that at wliich they are farthest apart is the 

 middle of the zooecium, occupied by the polypide and sexual organs. 

 The outlines of the young zooecia are straighter, and their breadth is 

 considerably less than that of the adult. 



From what we have already seen, the method of growth of the stock is 

 perfectly evident : it is by the formation of new median buds at the tips 

 of existing branches, and of new branches from lateral buds. In order 

 to understand the origin of the individuals of the primary branches, to 

 which suliject we will first turn our attention, we must study the tips 

 of the branches. 



2. Histology of the Budding Region. 



Figures 7-9 will serve to show more in detail the method of formation 

 of new terminal individuals. We find in these cases one polypide already 

 pretty well developed and attached to the body wall by means of the kamp- 

 toderm at about the point at which the pyramidal muscles {mu. pyr.) 

 are seen to be forming. That portion of the animal which extends from 

 about the region of formation of the muscles to a point a little proxi- 

 mad of the tip represents the region which will go to form the new in- 

 dividual. The tip itself, for reasons which will presently ajipear, is not 

 to be included in the terminal individual. The tip of the branch is to 

 be regarded as homologous with the rnargin of the corm in corm-building 

 genera of Gymnola^mata. Figures 7-9 {gn.) also show the position of 

 the bud which is to produce the polypide. By consulting first Figure 9, 

 in which the polypide bud is apparent, the significance of the swellings 

 of the body wall in Figures 8 and 7 becomes clear. 



Figure 14 (Plate II.) represents a stage in the development of the 

 polypide bud, somewhat later than that shown in Figure 9, and this may 

 serve us as a starting point in our study of the origin of a new individual, 

 and, first of all, of the new polypide. The whole of Figure 14, from the 

 tip down to the neck of the older polypide {cev. pyd.), may be divided, for 

 convenience, into three zones : first, that distad of the young bud, which 

 may be called the tip of the branch (Fig. 14, a to ^) ; secondly, the region 

 of the bud itself, which may be called the gemmiparous zone (yS to y) ; and 

 thirdly, the region between this last zone and the neck of the older poly- 

 pide, which, for want of a better name, may be called the proximal zone 

 (y to 8). In the formation of a new polypide between a and ^, that 

 region will in turn become divisible into the three zones just named, 



