
No. 427.] NOTES AND LITERATURE. 589 
Dr. Helen Dean King.’ It was found that the removal of the oral 
end by a cut just below the tentacles was followed by the regen- 
eration of fewer tentacles than were possessed originally, while 
the diameter of the regenerated hypostome was less than that of 
the original hypostome. As this operation reduces the volume of the 
body, the result appears to agree with the view advanced by Parke? 
(p. 702), “that a certain ratio exists between the size of a Hydra 
and its number of tentacles, and that when this ratio is destroyed 
by an increase or decrease in size of the Hydra, there will be an 
increase or decrease in the number of tentacles of that Hydra.” 
When the tentacles were removed by cutting at the base of each 
one so as not to diminish the volume of the trunk, in most cases 
as many tentacles were regenerated as had been removed. 
The severed * heads" remodeled themselves into small polyps, 
and, although the hypostomes suffered reduction in diameter, in no 
case was a reduction in the number of tentacles observed, in spite 
of the smallness of the polyps. This, the author maintains, does 
not support Parke’s view. (It should be noted, however, that 
Parke’s statement was made with reference only to change of size 
resulting from favorable or unfavorable conditions, — not to decrease 
in volume by the mechanical removal of part of the body.) 
Double-headed forms were produced by splitting the oral end 
longitudinally. When the tentacles were first removed, the total 
number of tentacles ultimately borne by the two heads together 
was an average of 3.4 tentacles per hydra greater than the number 
originally borne. When the tentacles were not removed previous to 
the splitting of the oral end, the average number of new tentacles 
developed by the two heads together was 5.1 per hydra. These 
double-headed polyps resolve themselves into two polyps by what 
resembles a process of longitudinal division, the final separation 
occurring at the extreme aboral end. Some of these double-headed 
forms were made to attach themselves oral end downwards. The 
Separation of the two parts occurred at the aboral (upper) end as 
before, proving that the longitudinal fission is not due simply to the 
constant strain exerted by gravity at the point of divergence of the 
two branches of the trunk. 
1 King, Helen Dean. Observ d Experiments on Regeneration in 
Hydra viridis, Arch. pus TAREAS HR der Organismen, Bd. xiii, Hefte 
I and 2 (1901), pp. 135-178. 31 text-figs. 
? Parke, H. H. Variation and Regulation of Abnormalities in Hydra, Arch. 
Sir EEE E der Organismen, Bd. x, Heft 4 (1900), pp. 692-710. 
9 text-figs. 
