i ;| i (l l Torn ii : Regeneration of Hydranth and Holdfast. 209 



their greatest diameter more rapidly than the tentacle funda- 

 ments relatively to the diameter of the column, with which, in 

 general, the size of both is correlated. 



With the disappearance of the axial tissue in the ridges separ 

 ating tlie canals, and the formation of a continuous epithelium. 

 the second set of proximal tentacles arises, one by cue. between 

 and mi the same level with those of the first set. The number 

 in the latter usually ranges between twelve and eighteen, slightly 

 more than half the total number I 18-30) ■* and the canals together 

 ordinarily occupy a little more than half the surface of the stem. 

 The correspondence between number of tentacles and diameter 

 of stem is evident here. 



The distal tentacles develop in successive groups. In the 

 first group, they usually appear somewhat later than the first 

 proximal set."' in smaller number. The decrease in number is 

 correlated with certain differences in the conditions. Tin 1 stem 

 at the level of the distal tentacles is less in diameter than at the 

 level of tlie proximal tentacles, and partly because of this, the 

 canals are disposed to fuse more readily in this region. When 

 the canals are distinguishable, it may be seen that the first distal 

 tentacles arise, one on each, as did the proximal, in a single 

 whorl; succeeding tentacles appear after the canals have fused, 

 more or less irregularly and below the first. When the end of 

 tie- stem is much narrowed and the canals obliterated before any 

 tentacles have appeared, the latter may develop in quartettes, as 

 in the embryo, though the stem may be very much larger than 

 the embryonic stem. Several cases of this sort have been ob- 

 served, one of which is figured (fig. 5). The members of the 

 second quartette arise at. a slightly lower level than, and in 

 alternation with, the first four tentacles; as in the embryo, they 

 may appear singly or simultaneously. Apparently the quartette 

 method is the direct result of the size of the stem; only a limited 

 number of tentacles of a certain size arise on a limited surface. 

 The regenerating tentacles are much larger than the developing 



* In one instance, thirty-four tentacles were borne on a small regenerating 

 stem, more than I have ever seen in any other individual. 



s Their appearance may lie delayed in exceptional eases, until the 

 proximal tentacles have reached their full number. 



