128 DIFFUSION AND OSMOTIC PRESSURE 



that growth takes place more slowly in a concentrated solu- 

 tion than in a weaker one. Loeb 1 found that the regenera- 

 tion of decapitated tubularian hydroids occurs much more 

 slowly in a concentrated than in a dilute solution. The 

 optimum concentration lies considerably below the normal 

 concentration of sea- water, in which these animals live natu- 

 rally. Similar results were obtained by Yung, 2 working on 

 tadpoles, and also by J. L. Frazeur (with annelids) and P. E. 

 Sargent (with Dero vaga) in the laboratory of C. B. Daven- 

 port. 3 



The first of a very important series of observations dealing 

 with the effect of external concentration upon cell division 

 was made by Loeb* when he discovered the fact that, in fer- 

 tilized Arbacia eggs which were placed in sea-water whose 

 concentration had been raised by the addition of NaCl, the 

 nuclei divided a number of times without the usual accom- 

 paniment of the segmentation of the entire egg. When 

 these eggs with segmented nuclei were returned to normal 

 sea-water, segmentation of the cytoplasm occurred suddenly, 

 the number of segments corresponding, in general, to the 

 number of parts into which the original nucleus had divided. 

 Loeb concludes from these experiments that the extraction 

 of water by high osmotic pressure causes a falling off in the 

 irritability of the protoplasm. Whereas, a part of the nor- 

 mal process of cleavage, namely, that pertaining to the 

 nucleus, is carried out, the remainder of it, segmentation 

 of the egg, fails to occur in the strong solution. The cyto- 

 plasm fails to perform its part, although the nucleus is still 



1J. LOEB, Untersuchungen zur physiologischen Morphologic der Thiere. II: 

 Organbildung und Wachsthum, Wiirzburg, 1892. 



2 E. YUNG, " De 1'influence des variations du milieu physico-chimique sur le 

 developpement des animaux," Arch, des sci. phys. et nat., Vol. XIV (1885), pp. 502-22. 



3 C. B. DAVENPOET, Experimental Morphology, New York, 1899, p. 365. 



*J. LOEB, "Ueber Kerntheilung ohne Zelltheilung," Arch. f. Entwickl. d. 

 Organismen, Vol. II (1895), pp. 298-300. 



