
No. 427. CHANGES IN HYDRA VIRIDIS. 8 
593 
at the base of the tentacle, and interstitial cells were seen to 
be dividing quite rapidly in the tentacle itself. It would seem, 
on the whole, that new tissue is furnished to the tentacle by 
division of cells at the proximal end, or base, rather than by 
division of cells that have already entered into the new organ. 
With the exception of the formation of nettle cells from 
interstitial cells, it is not found that cells of one kind give rise 
to cells of another, but that neuro-muscular cells of the new 
hydra result from neuro-muscular cells of the piece, and inter- 
stitial from interstitial. 
Considering, therefore, that the first appearance of the ten- 
tacle may be unaccompanied by cell division in its immediate 
neighborhood ; that cell division, though frequently found in 
the region of the growing tentacle, is not confined to this 
region but is found elsewhere throughout the length of the 
regenerating piece ; that division is found to be present as late 
as seven days after the cutting, that is, after the piece has 
assumed the proportions of a normal hydra; and that some 
division is observed in the tissue of the normal, probably 
rapidly growing hydra, — we are justified, I think, in conclud- 
ing that the new cells which appear during the regeneration of 
hydra are formed by division of the old cells throughout the 
entire piece, as in the normally growing animal, and that the 
tentacles are formed from old cells and from cells that have 
arisen by division of the already differentiated cells of the old 
part. 
I am very much indebted to Prof. T. H. Morgan, under 
whose direction this work was carried on. 
Bryn Mawr, January, 1902. 
