Amount of Tail Regenerated to’ Removed-in Tadpoles 445 
per cent regenerated. In Experiments 2 and 3, for example, 
the various per centums, from zero to fifty, were regenerated by 
the several series, although the tadpoles comprising these were of 
the same age. This difference was due to the effect of tempera- 
ture; and similarly other factors may be shown to influence the 
amount regenerated. A confirmation of the hypothesis, that the 
age or state of development does influence the amount regenerated 
and that the more nearly the adult condition is reached the lower 
the rate of regeneration, occurs in the following Table, constructed 
from the percentages regenerated in Experiments 6, 7, and 8, 
which were subjected to the same conditions. 
TABLE 8 
AVERAGE BODY LENGTH PER CENT 
mm. REGENERATED 
YC PETLMEN Or. aren un As ele piel ners sieve Ae asa 19 55 
LDyee(saniel sae jrin cou soba po Obese eo arc 29 5° 
BS PETUNENE Oc toatcle ee.se sl dats Oe icin vie 45 46 
These comparisons are, perhaps, not absolutely accurate, since, 
as explained in the first part of this paper, body length had to be 
taken as an index of the age or state of development; but allowing 
for this inaccuracy, there are definite differences between the 
amounts regenerated by the tadpoles of various sizes under the 
same conditions. 
At this point, the process of regeneration itself should be con- 
sidered. Regenerated tissue is the direct product of cell division, 
and accordingly, the rate of regeneration is dependent largely 
upon the rate of cell division. According to Morgan’s tension 
theory, the cell tends to divide until the external (that is, extra- 
cellular) pressure and tension are equal to the force within itself, 
causing it to divide. When these forces are equal, differentiation 
begins. Minot and others have shown that the more embryonic 
the cell, the more it tends to divide; in other words, the greater 
this force which prompts the cell to divide despite extra-cellular 
forces. ‘The tail of a tadpole is an embryonic organ; hence, prob- 
ably contains large numbers of embryonic cells. As previously 
mentioned, Kammerer found the rate of regeneration to vary with 
