386 | C. M. Child 
ment of a new polarity. Analysis of the regulatory processes in 
these rings seems at present to afford strong evidence in favor of 
this view. 
6 Origin and Structure of Oral-Aboral Tentacles 
The frequent occurrence of oral-aboral tentacles along the line 
of union in the rings has been noted in the descriptive section of 
the paper. They occur in most of the groups which involve both 
sides of the line of union, and may be either simple like other ten- 
tacles or forked. In the figures of the first series of rings (Figs. 
6 to 20) simple oral-aboral tentacles appear in the following cases: 
in the left-hand tentacle group in Fig. Io the tentacle at each end 
of the group is oral-aboral, though apparently belonging more to 
the oral side than to the aboral; in groups b c, and dof Fig. 12 the 
two lateral tentacles are oral-aboral in each case, and in group a 
the two tentacles of medium length. In the case shown in Fig. 
15 more oral-aboral tentacles than oral are present, for the two 
lateral tentacles in each group are oral-aboral; finally oral-aboral 
tentacles are present in each of the groups in Fig. 17, as shown by 
the detail figures 18 to 20. In Fig. 18 tentacles 1 and 4 are oral- 
aboral, in Fig. 19, 1 and 3, and in Fig. 20, 1 and 3. In these 
three groups all of the oral-aboral tentacles except No. 4, Fig. 
18, arise largely or wholly on one side or the other of the line of 
union, instead of upon it, as in most cases (Figs. 10, 15, 16). 
Nevertheless a valid reason for regarding them as oral-aboral 
tentacles is to be found in the fact that each arises over an inter- 
mesenterial chamber bounded by what was originally the oral end 
of one mesentery and the aboral end of another. 
Forked or branched oral-aboral tentacles occur in Fig. 8 (a and 
b) and in the right-hand group in Fig. 10. 
The appearance of these oral-aboral tentacles constitutes a 
demonstration of the fact that the original polarity and radial 
symmetry are almost or quite obliterated and a new polarity and 
symmetry established. The formation of a tentacle like those 
of the normal animal in form and function, so far as can be deter- 
mined, from tissue arising in part from the original oral end, in 
