EXPERIMENTS ON CLEAVAGE 261 
physiological conditions for segmentation of the nucleus are 
different from the physiological conditions of the segmenta- 
tion of the protoplasm. We now can be positive in this 
regard, as under the same conditions the nucleus continues 
segmenting, while the protoplasm does not show the slightest 
trace of segmentation. But these experiments allow us to 
go one step farther and to make clear one element in the 
complex called segmentation, namely, the physiological cause 
for the segmentation of the protoplasm. We saw that in the 
concentrated solution the protoplasm did not segment, while 
as soon as it was brought back into the normal sea-water it 
segmented at once into about as many cleavage spheres as 
nuclei were formed. All further inferences depend upon 
our knowledge of the effect of salt solutions on protoplasm. 
I have investigated this point myself, and have caused others 
also to take up this question. The result of all investigations 
hitherto carried on is as follows: Raising the concentration 
of the salt solution in which an animal or a tissue lives has 
the same effect as lowering the temperature; lowering the 
concentration has qualitatively and quantitatively the same 
effect as raising the temperature. I will mention two cases 
to illustrate this. First, one example to show the parallelism 
of the mentioned effect of the temperature and the concentra- 
tion in qualitative regard. JI have recently succeeded in 
making animals belonging to different classes—larve of 
Polygordius, Copepods, etc.— positively heliotropice by bring- 
ing them into low temperatures, and making them negatively 
heliotropic by raising the temperature of the water. In water 
from 0° toabout 10° larvee of Polygordius, for instance, are 
exclusively positively heliotropic. In water above 25° they 
are exclusively negatively heliotropic. But by adding a 
certain amount of NaCl to normal sea-water I was able to 
make them just as well positively heliotropic, and by adding 
a certain amount of fresh water to the normal sea-water I 
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