336 STUDIES IN GENERAL PHYSIOLOGY 
ther insight into the nature of these ultimate elements will 
consequently be dependent upon a knowledge of this order. 
This significance of the quantity of living substance as 
the carrier of a definite amount of energy is also apparent 
in the regeneration of multicellular animals. According to 
the experiments of Nussbaum, “at least one ectoderm, one 
entoderm, and one cell from the intermediary germinal layer 
is necessary” for the regeneration of a Hydra capable of 
reproduction. But this minimum gives us only a qualita- 
tive limit, in so far as the three qualitatively different ele- 
ments are necessary. So far as the quantity is concerned, 
it must be said that a very large multiple of each of these 
three elements is necessary for regeneration. In experi- 
ments on Tubularia which Miss Bickford made in my labo- 
ratory two years ago’ it was found that pieces 1 mm. long 
from the stem of this Hydroid are.no longer able to regener- 
ate into complete Tubularie; either only a simple polyp 
without stem and root is formed, or a peculiar heteromor- 
phous formation, a sort of Janus head, occurs, consisting of 
two polyps connected with each other by their aboral ends, 
while the stem and root are missing between them. 
That the smallest amount of matter capable of develop- 
ment must have a different absolute size in different organ- 
isms—that, for example, it must be smaller for a coccus 
than for an Arbacia egg—need not be specially mentioned. 
10. The results of our observations are briefly as follows: 
a) The limits of divisibility of living matter must vary 
according to the character of the life-phenomena used as 
a criterion of life. Each quantity of living matter is the 
bearer of a definite quantity of energy. 
b) The smallest fraction of an. unsegmented egg of 
Arbacia necessary for the formation of a pluteus is about 
lArchiv fiir mikroskopische Anatomie, Vol. XXXV (1890). 
2K. Bickrorp, Journal of Morphology, 1894. 
Digitized by Microsoft® 
