496 C. M. Child 



the case of Series I of Table I the decrease in length of the ten- 

 tacles between fourteen and twenty-six days is a part of this regu- 

 latory process. The growth of these tentacles was so rapid that 

 they attain a much greater length than the tentacles of the other 

 series, consequently as the altered environment made itself felt, 

 the tentacles in Series I were much more affected by it than those 

 of the other series, which had grown more slowly. 



To sum up: my observations on the regional differences in oral 

 restitution in Harenactis show that rapidity of formation and 

 growth in length of the new tentacles decrease proximally in the 

 body; that the amount of tentacle-restitution is not proportional 

 to the size of the piece nor directly correlated with the region of 

 the body, for smaller pieces produce relatively longer tentacles 

 than larger, even though the level of restitution may be much 

 farther proximal in the former than in the latter. 



Attention may be called in passing to the fact that in pieces of 

 very different length, but with oral ends at the same level of the 

 body, the rapidity and amount of tentacle-restitution are approx- 

 imately the same, except when the differences in size are extreme, 

 in which case the tentacles of the smaller piece do not attain quite 

 the length of those of the longer piece. In Harenactis the results 

 in small pieces are often complicated by the extrusion of enteric 

 organs, so that it is difficult to obtain satisfactory data for pieces 

 of very small size. In general the regional differences in rapidity 

 and amount of tentacle-restitution and the relations between 

 amount of restitution and size of piece are much the same in 

 Harenactis as in Cerianthus (Child '03b): the later series of data 

 confirms the earlier. 



Regional Differences in the Number of Tentacles 



In normal individuals of Harenactis the number of tentacles and 

 mesenteries is twenty-four: the tentacles form a single row about 

 the margin of the disc and arise as is usual over the inter-mesen- 

 terial chambers. The twenty-four mesenteries are arranged in 

 twelve pairs, consisting of two cycles of six pairs each, the mem- 

 bers of the two cycles alternating with each other (Torrey '02). 



