REGENERATION IN HYDRACTINIA AND 
PODOCORYNE. 
ANNAH PUTNAM HAZEN. 
In a paper entitled “ Experiments in Regeneration and in 
grafting of Hydrozoa,”! Peebles has given the results of some 
interesting experiments with Hydractinia and Podocoryne. 
These two hydroids are found at Woods Hole on the shells 
inhabited by hermit crabs. Each colony consists of three 
different kinds of individuals, namely, the nutritive, the repro- 
ductive, and the protective (a low cone-shape growth extend- 
ing over the hydrorhiza is considered by some authors to 
constitute a fourth class of individuals). The experiments 
described by Peebles were confined to the first three classes. 
The well-marked characteristics of the different kinds of indi- 
viduals make it possible to distinguish between them even 
when the polyps are immature or incompletely regenerated. 
The knoblike tentacles of the reproductive polyps appear dur- 
ing regeneration earlier than the reproductive organs, and the 
long, slender tentacles of the nutritive polyps can be easily 
distinguished from those of the protective individuals, which 
contain nematocysts. Peebles found that polyps freed from 
the hydrorhiza would live for days in small dishes containing 
sea water and quickly regenerate lost parts. _ Pieces of the stalk 
of these three classes of polyps, from which the heads had 
been cut, regenerated new heads of the same kind as those 
that had been removed. Small pieces cut at different levels 
from the stock of nutritive and protective polyps regenerated 
at one end a head like the one removed. Not infrequently a 
head appeared at both ends of a short piece, Without exception, 
the regenerated heads had the same characteristics as those that 
had. been removed, and no constant variation in time or capacity 
for regeneration at the different levels was observed. 
1 Archiv für Entwickelungsmechanik der Organism, Bd. x, Hefte 2, 3. 
