384 C. M. Child 
regions where tentacles have already appeared on the oral end: 
this is evident from Figs. 6and 8,and 11 and 12. The only pos- 
sible interpretation of these cases seems to me to be that the aboral 
end has become more oral physiologically in consequence of its 
union with the oral end or, in other words, the original polarity 
has been largely eliminated because the correlations have been 
altered. The other two cases of the first series differ from these 
only in the simultaneous appearance in most cases of the tentacles 
on both sides of the liné of union (Figs. 15, 16 and 17 to 20). 
In the second series, in which the tentacles appear wholly on the 
oral side of the line of union, that part of the group which lies 
nearest the line of union often appears later than the other parts 
and remains of smaller size. Such a case is shown in Fig. 23 which 
represents group b of Fig. 22 and the other groups of this ring are 
similar; in Fig. 24, groups a and c, two tentacles on the side nearest 
the line of union appear later and are smaller than the others, and 
in group 0 the fourth tentacle which lies on the side toward the 
line of union does not appear at all until after the stage shown in 
Fig.24. Fig. 25, group ), and Fig. 27 show this group as it appears 
after the fourth tentacle has developed. 
In these cases the part which lies nearest the original oral end 
of the piece develops tentacles more slowly than other parts. 
Apparently in these cases the development of these tentacles 1s 
delayed either because union of the oral with the aboral end affects 
the oral end, as it has been shown above to affect the aboral end, 
but in the reverse direction, or else the reversal of symmetry which 
is involved in the formation of these tentacles requires a certain 
amount of time, or both of these factors may be involved. [am 
inclined at present to believe that the effect of the aboral upon the 
oral end may be the more important in determining the rapidity 
of development of the tentacles in question. Since the aboral end, 
which otherwise never produces tentacles, becomes capable of 
tentacle-production when united with the oral end in these rings, 
it is not at all improbable that the physiological condition of the 
oral end is altered by its union with the aboral end, but in the re- 
verse direction. If this is the case, the union of the two ends 
decreases the differences between them, i. e., the polarity. It is 
