14 BULLETIN OF THE 
the formation of the body wall by the neck of the polypide is much 
smaller than Braem has suggested, and probably insignificant in amount. 
The retreat of the points of origin of the retractor and parietovaginal (py- 
ramidal) muscles may be in part accounted for by the normal growth in 
area of the body wall, and in part by the actual movement of the point 
of origin with reference to the cells of the body wall. These conclusions 
rest upon the following circumstantial evidence, 
Owing to the small number of cells in the body wall at the tip, and 
the comparatively slow growth of the cystid, karyokinetic figures are 
much less frequent than in the polypide. Quite a long search has there- 
fore not afforded cases enough to enable me to draw any perfectly satis- 
factory conclusions as to just where, and where only, growth was taking 
place. I have, however, seen nuclear division occurring in the elongated 
cells of the extreme tip, rather more abundantly in the cuboidal cells 
between the extreme tip and the gemmiparous zone, and most abun- 
dantly in the gemmiparous zone, but here evidently having to do with 
the origin of the polypide, muscle cells, etc. Proximal to the gemmipa- 
rous zone, I have noted few cases of nuclear division excepting about 
the neck of the polypide. It seems probable that the cells of the tip 
of the branch are not to be regarded as forming a differentiated organ 
whose elements rarely divide, but as quite capable of adding new cells to 
the body wall. On the other hand, there is by no means a Scheitel in the 
botanical sense, but the cells added to the body wall continue for a time 
to divide vigorously, and finally give rise to the polypide, to the Anlage 
of the lateral branches, and to the body wall. The cells belonging to 
the proper cystid then cease to divide rapidly. 
I have already shown how the cells of the tip secrete a cuticula, which 
becomes gradually replaced by a second cuticula secreted beneath it as 
the body wall attains its adult dimensions. It appears as though the 
first cuticula were secreted by the cells of the tip only. This being so, 
since the area ‘of the body wall increases, this first cuticula must either 
stretch to cover the enlarged area, or else it will fail to cover it and 
appear as isolated patches upon the body wall, and these isolated patches 
will become more and more widely separated as the area of the body 
wall increases. This latter condition seems to be the one realized in this 
case. The presence of the old cuticula is easy to demonstrate, since it 
stains deeply in hematoxylin ; and it may be easily distinguished from 
that formeil later, for with the same reagent this stains not at all. Figures 
6, 11, 12, and 13 show different appearances of the cuticula at different 
parts of the body wall. At the extreme tip (Fig. 6) there is a continu- 
