
No. 427.] CHANGES IN HYDRA VIRIDIS. 581 
dividing. Where so many cells were about to divide or had 
just completed division, we should expect to find a correspond- 
ing number undergoing the actual process. This, however, 
was not the case. 
A further point should also be kept in mind, vzz., the possi- 
bility that multiplication of the interstitial cells may be con- 
cerned with the development of new nematocyst cells rather 
than with the regeneration of new tissue. 
In order to get more light on these points, the tissue of a 
normal hydra was examined for comparison with that of the 
regenerating piece. Another hydra was irritated with a blunt 
needle in order to induce it to discharge the nettle batteries. 
It was then left undisturbed for about twenty hours, at which 
time it was killed and the tissue prepared as has been described. 
It was hoped by these means to obtain further light on the 
difficulties of the question, and to be able to distinguish more 
clearly between the phenomena of regeneration and those 
merely incidental to the formation of new nettle cells. 
In the case of the stimulated hydra, nettle cells were found 
to be forming as in the regenerating pieces. Moreover, in the 
tissue of this hydra and of the undisturbed normal one also I 
was surprised to find undoubted evidence of cell division, in 
addition to the very general loose and broken appearance of 
the chromatin in some of the interstitial cells, which has been 
noted as occurring in the regenerating piece. This latter con- 
dition, found in a hydra upon which no operation had been 
performed, made it still less possible to consider such nuclei 
as dividing. On the other hand, a piece that had been regen- 
erating seven days, and that had attained to the proportions 
of a normal polyp, was found to present the same appearance 
under the microscope. It is possible, therefore, that the normal 
tissue examined was that of a growing hydra, and that these 
conditions are common to the regenerating and growing forms, 
while further examination of the tissue of fully grown hydras 
might show a somewhat different state. 
While these latter experiments, therefore, threw little light 
on the amount of division in the regenerating piece, yet the 
similarity in appearance between this regenerating tissue, the 
