No. 2.J PHYSIOLOGICAL MORPHOLOGY. 259 



ized in normal sea-water and which were put in the concen- 

 trated solution, after being brought back into normal sea- water 

 for from ten to twenty minutes segmented without any exception 

 and were able to develop into normal planulae and plutei. Eggs 

 of this kind were still able to develop into normal larvae after 

 having been in the concentrated solution for four or six hours. 

 But eggs which before impregnation had been put into the con- 

 centrated solution together with spermatozoa, and which four or 

 six hours later were brought back into normal sea-water, reached 

 only the first stages of segmentation, if they segmented at all, 

 and then stopped developing. I never got a living larva from 

 these eggs. From all these facts I conclude that the continual 

 increase of the nuclei of the impregnated eggs in the concen- 

 trated solution was due not to polyspermia, but simply to seg- 

 mentation of the nucleus. In these experiments somewhat 

 bacteriological precautions are necessary, as the water of the 

 aquarium is liable to contain quantities of spermatozoa. 



7. From the above I believe to have shown that, by bringing 

 fertilized eggs of sea-urchins into more concentrated sea-water, 

 — we added 2 to 2.4 g. NaCl to 100 ccm. sea-water, — the seg- 

 mentation of the nucleus proceeds, although more slowly than 

 under normal conditions, whilst no segmentation of the proto- 

 plasm is possible. The fact in itself is of some technical value, 

 as it enables us to separate two processes which nature gener- 

 ally produces together, or which hitherto we had not the power 

 to separate at desire. In regard to our knowledge of segmenta- 

 tion, we see from this that the physiological conditions for seg- 

 mentation of the nucleus are different from the physiological 

 conditions of the segmentation of the protoplasm. We now 

 can be positive in this regard, as under the same conditions the 

 nucleus continues segmenting, whilst the protoplasm does not 

 show the slightest trace of segmentation. But these experi- 

 ments allow us to go one step farther and to make clear one 

 element in the complex called segmentation, namely, the physio- 

 logical cause for the segmentation of the protoplasm. We 

 saw that in the concentrated solution the protoplasm did not 

 segment, whilst 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 proto- 



