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: Kaising 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. I have recently succeeded in 

 making animals belonging to different classes larvae of 

 Polygordius, Copepods, etc. positively heliotropic by bring- 

 ing them into low temperatures, and making them negatively 

 heliotropic by raising the temperature of the water. In water 

 from to about 10 larvae 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 



