DR. E. B. WILSON ON THE DEVELOPMENT OF RENTLLA. 
795 
the zooid x. of fig. 202. The three other zooids are evidently placed with reference to 
p u . and not to p 1 . Thus the zooid d". has its ventral chamber turned towards the 
centre of the main group and away from that of the secondary group. Hence d". is 
the offspring of p 11 . and the grandchild of p 1 . 
There appear to be in fig. 203 two other secondary centres, but each is repre¬ 
sented by two or three zooids only. Thus a, b, and c seem to be arranged about the 
centre y, while d', e, and perhaps f, are arranged about a centre at 2 . It is rare to find 
the secondary groups completely or symmetrically formed, and in many, perhaps most, 
cases no secondary centres can be certainly identified. In fact, I have seen only two 
cases in which the secondary groups were as perfectly formed as at x. in fig. 203. 
Review. 
The close correspondence between the mode of budding of the zooids and of the 
sexual polyps must already have struck the attention of the reader. If the group of 
four zooids shown in fig. 199 be compared with the group consisting of three sexual 
polyps and the exhalent zooid (fig. 181) the composition of the two groups is found to 
be the same. If the axial polyp in fig. 181 be turned upwards at its anterior part, as 
actually happens at a later stage, it will have the same relation to the exhalent zooid 
as that existing between the lower and upper zooids of fig. 199, and the two lateral 
buds in fig. 181 when turned upwards have precisely the same position as the lateral 
zooids in fig. 199. 
Similarly, we may compare the group of eight zooids (fig. 202) with the groups of 
eight shown in figs. 184, 205 and 206 (these are seen from the ventral side so that 
the dorsal member of the group, the exhalent zooid, does not show directly). It is 
scarcely necessary to remind the reader that I do not mean that the corresponding 
members of the two groups are homologous with each other, but only that they have 
been produced by a similar form of asexual multiplication. 
Summing up these results, we find that the multiplication of the zooids conforms 
to a definite law, which upon comparison is found to be identical with that which rules 
the budding of the sexual polyps. 
§ 18. Closure of the peduncular canals. 
We have finally to describe the manner in which the two canals of the peduncle 
become closed in front and thus complete the canal-system. As described in the 
introduction, these canals are in the adult completely closed in front, whereas in the 
young they communicate freely with the gastric cavity of the axial polyp. 
a. The dorsal canal. 
The closure of the dorsal canal is effected by the free edge of the peduncular septum 
growing forwards and finally uniting with the dorsal wall just anterior to the exhalent 
