No. 33] TUBULARIAN HYDROIDS. 4 
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7 
IV. REGENERATION OF LONGITUDINAL SECTIONS OF 
TUBULARIA. 
It remained to be seen whether results similar to those 
described, could also be obtained from longitudinal sections. 
Trembley experimented upon Hydra, cutting them in halves 
lengthwise ; he stated that healing occurs so rapidly that in 
three hours they were able to eat as usual. In this case there 
was evidently only a closing of the wound, and not a formation 
of new parts. The experiments to determine the ability of 
split portions of the coenosare to form hydranths, were made 
as follows :— 
Several good-sized stems were cut open longitudinally; 
some of the fragments thus obtained were very small and 
narrow, other stems were only partly split. These were exam- 
ined the next day, and all the portions of coenosarc, even the 
smallest, were healed and rounded in form; they showed a 
most vigorous circulation within (see Fig. 23). When exam- 
ined later, most of these portions had not regenerated ; one 
stem was found, however, which presented the following inter- 
esting conditions (see Fig. 24): it had been split ouly half 
way down, the lower portion of the stem remaining whole. 
On the two split portions of the perisarc there were four 
separate rounded masses of coenosarc, each of which had 
regenerated, two with hydranths directed aborally and two 
orally, while from the point of union of the two, a fifth good- 
sized hydranth had appeared. As usual, the sizes of these 
hydranths were proportional to the diameters of the masses 
from which they were formed. 
From these experiments it may be concluded that, while 
split portions may regenerate, yet this does not take place as 
readily as is the case with transverse sections. In all cases 
they pass through the first stages of regeneration, healing very 
readily. The fact that they are unprotected by the perisarc, 
and thus left exposed to the action of the water, may account, 
in part, for their failure to regenerate completely. 
