358 C. M. Child 
turned more or less toward the observer in order to show more 
clearly the arrangement of tentacles. 
Cases with Tentacles on Both Sides of the Line of Union 
The following cases are selected from among a much larger 
number as illustrations of the results in such rings. No two indi- 
vidual cases are alike but the cases described are sufficient to show 
the principal features. 
I Figs. 6 to 9. Piece from the region just proximal to the 
cesophagus: after section some portions of the mesenterial organs 
extruded through cut ends and removed, but a considerable bulk 
of these organs remained. Piece closed by union of oral and ab- 
oral ends, forming a ring. ‘Tentacles began to appear eight or 
nine days after section. Fig. 6 shows a stage eleven days after 
section. ‘The line of union between oral and aboral ends is at the 
equator outside and is therefore not visible. ‘he tentacles pres- 
ent are all developing from the original oral end. Fig. 7 represents 
a section in the plane of the broken line in Fig. 6; here the thin 
new and redifferentiated tissue at the region of union and the 
position of the tentacles with reference to it are indicated. 
Fig. 8 shows the piece seven days later. Fig. g is a section of 
the stage of Fig. 8 in the plane of the broken line. A change in 
position of the region of union has occurred in consequence of the 
revolution of the tissues of the ring about a circular axis as above 
described, and the region of union now lies at what might be called 
one of the poles of the ring, 1. e., half way between the equatorial 
region on the periphery and that in the central opening. The 
number of oral tentacles is the same as before but their length 
has increased and the change in position of the oral end has appar- 
ently altered their relation to other parts. Comparison of Figs. 
7 and g shows the character of this change. The revolution has 
occurred in the direction of the arrows in Fig. 7 and hasbrought 
the region of union into the position shown in Fig. 9. But the 
most interesting feature of Fig. 8 is the appearance of tentacles 
on the aboral side of the line of union. Five aboral tentacles are 
present at this stage; two of the oral tentacles bear branches near 
