254 Experimental Zoology 
way in Minot’s experiments with pregnant guinea pigs not fully 
grown. Not only did the mother grow at the normal rate, but 
she supplied the embryo also with a large amount of nourish- 
ment. 
We can account for the facts on the assumption that when less 
than the optimum is given more substance is digested from the 
food, and when more than the optimum is taken proportionately 
less is absorbed or assimilated. The appetite of the animal fur- 
nishes in a measure an index of the amount needed for growth 
and repair, but one that cannot be entirely relied upon. 
The size of the adult stage of some of the lower animals is 
much affected by the amount of food that can be obtained. 
There is, however, an upper limit that is quickly reached when 
food is abundant that cannot be surpassed. Most of the varia- 
tion in size lies below this condition. For example, fresh-water 
planarians if kept without food for several months decrease in 
size, and finally may be not more than about 1/15 of the original 
volume. If such a starving worm is cut in two, each piece still 
has the power to regenerate the missing part, drawing on or 
making use of the starving tissues in order to make the new 
growth. Thus, although the worm is starving it will grow rela- 
tively rapidly at the cut surface and produce a new part. If 
a starving earthworm is cut in two in the middle, the anterior 
piece makes a new tail, and the posterior piece also regenerates 
a tail (reversed in direction) at the anterior end of the piece. 
In the latter case the old part continues to waste away, while 
the new reversed tail continues to add new segments to its grow- 
ing end. Thus while starvation is taking place in the old piece, 
growth goes on in the new, and the latter must derive all of its 
material from the starving portion. In the “winter” salmon of 
the Rhine the tissues of the body are used as food after the fish 
have entered fresh water, when they cease to feed. These sal- 
mon may live for months (from 8 to 15, according to Meischer) 
without food. At the end of this time the fish are much emaci- 
ated. During the period of starvation the eggs develop. There 
can be little doubt that a starving mammal, if pregnant, would 
