514 ABSTEACTS OF MEMOIRS. 



The Influence of Osmotic Pressure upon the Regeneration of Gunda 

 uluce. By Dorothy Jordan Lloyd, B.Sc. {Proc Boy. Soc, B, 

 Vol. XXVII, 1914.) 



The animals used in the experiments recorded in this paper were collected 

 from the shore near the borders of a small stream and between the 

 tide-marks. They were therefore exposed in their natural habitat to a 

 wide diurnal variation of osmotic pressure. Experiments made with 

 whole animals showed that they are capable of living indefinitely in 

 water having an osmotic pressure of more than two and less than thirty- 

 three atmospheres. Experiments on the rate of regeneration of the 

 posterior end only were considered. These showed that the rate of 

 regeneration of the posterior end depends on the osmotic pressure of the 

 medium. This has an optimum value at eighteen atmospheres, and 

 limiting values at five and thirty-five atmospheres. 



Restoration of the lost paiis in G. ulvce is brought about entirely by 

 the undift'erentiated parenchyma cells, which migrate to the region of 

 the wound and form the new tissues. The growth of the new parts is 

 always accomp: nied by reduction of the old ones. For values of the 

 osmotic pressure lying between the optimum and the limiting values 

 the migration of the parenchyma cells is retarded, and the rate of restora- 

 tion is retarded to a s'milar degree. At the hmiting values there is no 

 migration and no restoration of lost parts. 



G. ulvce also shows the phenomena of reduction under conditions 

 of starvation. These are (1) absorption of the genital system, (2) general 

 reduction in size. Both of these changes are brought about by the 

 phagocytic action of the parenchyma cells. During regeneration the same 

 reduction processes occur as in starvation. When the restoration of lost 

 parts is retarded, as happens on raising or lowering the osmotic pressure, 

 reduction is retarded to the same extent. 



In strongly hypotonic solutions the gut cells increase in size and become 



vacuolar ; in strongly hypertonic solutions they diminish in size and 



become dense, showing that there has been actual gain or loss of water by 



the tissues. 



D. J. L. 



