VII 
EXPERIMENTS ON CLEAVAGE! 
1. In the second part of my Untersuchungen zur physio- 
logischen Morphologie? I showed that regeneration and 
growth in animals are, as in plants, a function of the amount of 
water contained in the cells. When I increased the amount of 
water in the cells of Hydroids by bringing these organisms 
into more diluted sea-water than that in which they usually 
live, the rate of growth increased with the decrease of the con- 
centration of the sea-water. When I diminished the amount 
of water in the tissues of Hydroids by bringing these animals 
into a more concentrated solution than the normal sea-watec, 
the rate of growth diminished too. We know that seedlings 
of plants need water in order to develop. It is the same in 
the animal egg, as recent investigations concerning the 
development of sea-urchins, starfish, arthropods, and fish 
showed me. If we reduce the amount of water contained in 
the egg of the sea-urchin by bringing it into more concen- 
trated sea-water, the process of segmentation is retarded 
only as long as the increase in the concentration is small. 
As soon as the concentration is greater, however, the fertil- 
ized egg does not segment at all. In one case the eggs had 
been fertilized at 9:40 a.m. A few minutes after the impreg- 
nation, one part (a) of the eggs were put into sea-water to 
which 1 g. of NaCl to 100 ¢.c. had been added. A second 
part (b) were put into sea-water to which I had added 1.3 g. 
of NaCl to 100 c.c. A third part (c) were brought into sea- 
water, the concentration of which was increased by the addi- 
tion of 2 g. of NaCl to 100 c.c.; and a fourth part (d) 
1 Journal of Morphology, Vol. VII (1892), p. 253. 
2Wiurzburg, 1892. Part I, p. 191. 
253 
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