262 



WALTER E. GARREY. 



TABLE IV. 



centration of the external medium. In these experiments with 

 dilute solutions it was found that when Venus was placed in fresh 

 water it closed up so tightly that after two weeks' immersion the 

 osmotic pressure of the blood was not lowered ; perforation of 

 the edges of the shell however admitted the fresh water and the 

 osmotic pressure was lowered. A lobster placed in 3 vol. sea 

 water -f I vol. distilled water showed a lowering of the osmotic 

 pressure, as indicated by J = - - 1.46. Marine flat worms on 

 the bodies of Limuli became much swollen in the diluted sea 

 water although they remain active for a long time. 



Concentrated sea water obtained by evaporating until J = 

 3.80 was next used as the medium of immersion. The blood 

 of Liinulus after sixteen hours in this medium froze at 3-79- 

 The blood of Houiarus in this doubly concentrated sea water 

 froze at - 3.60 at the end of eight hours. In sea water con- 

 centrated to 0.8 its original volume the blood of Homants froze 

 at 2.17 after two hours' immersion. These animals tolerate 

 an increased osmotic pressure much better than the equivalent 

 decrease. When the aquarium water is concentrated, complete 

 equalization of enormous differences in the osmotic pressure 

 between the external and internal media may take place without 

 any marked symptoms of asthenia such as are seen when the 

 external medium is dilute. 



From the facts just sketched we see that all of the marine 

 invertebrates which we have worked with are truly " poikilos- 

 motic." Two factors may be at work in producing the variations 



