INVESTIGATIONS IN PHYSIOLOGICAL MOR- 

 PHOLOGY. III. , , 



An b«. C- I a. 

 Experiments on Cleavage. 



jacques loeb, m.d., 



Assistant Professor of Physiology, University of Chicago. 



I, In the second part of my Unterstickungen zur Physiolo- 

 gischen Morphologic'^ I showed that regeneration and growth 

 in animals is, 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 in more 

 diluted sea-water than that in which they usually live, the rate 

 of growth increased with the decrease of the concentration of 

 the sea-water. When I diminished the amount of water in the 

 tissues of hydroids by bringing these animals into a more con- 

 centrated solution than the normal sea-water, 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, star- 

 fish, 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 concentrated 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 fer- 

 tilized egg does not segment at all. In one case the eggs had 

 ID'.Q'^ '^ been fertilized at 10.40 a.m. A few minutes after the impreg- 

 V (,'i> ^ nation, one part (S)~oIlhe eggs were put into sea-water to which 

 I g. NaCl to 100 ccm. had been added. A second part {b) 

 was put into sea-water to which I had added 1.3 g. NaCl to 

 100 ccm. A third part {c) was brought into sea-water, the con- 

 centration of which was increased by the addition of 2 g. NaCl 

 to 100 ccm., and a fourth part {d) remained in normal sea-water. 

 At 10.50 nearly all the eggs which had remained in normal sea- 



^ Wurzburg, 1892. Hertz, publisher. 



253 



