No. 2.] PHYSIOLOGICAL MORPHOLOGY. 261 



the same cause is quantitatively less. That explains how the 

 segmentation of the protoplasm is generally determined, why 

 in a solution of a certain concentration no segmentation of the 

 protoplasm takes place, and why when brought back into nor- 

 mal sea-water the protoplasm segments at once into about as 

 many spheres as there are nuclei pre-formed. T/ie segmenta- 

 tion of the protoplasm is the effect of a stimtilus which the nucleus 

 applies to the protoplasm, and which makes the protoplasm close 

 around the nucleus. If we bring the fertilized egg in the concen- 

 trated salt solution (2 g. NaCl; 100 sea-water) the nucleus divides 

 and every nucleus applies the stimulus to the protoplasm with 

 which it is in contact. But the protoplasm of the Q.g^, on 

 account of its containing too little water, is in the condition of 

 a cooled-off muscle, which does not answer to the stimulation of 

 the nerve, and no segmentation of the protoplasm takes place. 

 But as soon as we bring the ^g'g back into normal sea-water, the 

 protoplasm takes up water very fast and regains its irritability ; 

 and now, of course, it answers to the stimuli from the nuclei, and 

 closes around every nucleus or segments. If we add a smaller 

 dose of NaCl, namely, 1.3 g. NaCl to 100 ccm. sea- water, the 

 irritability is only little less than it is normally, and the whole 

 effect is that the reactions of the protoplasm are somewhat 

 slower and retarded. Of what kind the stimulus is and from 

 which part of the nucleus it is exercised, we cannot tell. From 

 other facts I am inclined to believe that this stimulus is a chem- 

 ical one, and caused by certain substances produced in the nu- 

 cleus which also may be effective if separated from the nucleus. 

 8. The physiological causes of the segmentation of the 

 nucleus are not directly touched by these experiments. But 

 two points ought to be mentioned : first, that the segmentation 

 of the nucleus in the concentrated solution (2 g. NaCl ; icx) ccm. 

 sea-water) was retarded, and at last ceased entirely after from 

 twelve to twenty-four hours ; secondly, that the segmentation of 

 the nucleus was extremely irregular when the protoplasm did 

 not take part in segmentation. We see in these facts some of 

 the influences which the protoplasm exercises on the segmenta- 

 tion of the nucleus. This influence may be exercised in this way, 

 — that by the high intracellular pressure which normally exists in 

 the cleavage spheres these spheres press and flatten each other. 

 The form of the cell, however, determines as Sachs showed 



