172 



J. F. ABBOTT. 



hours. Death appears to be due to a loss of necessary salts by 

 diffusion out of the body fluids together with a disturbance of 

 vital equilibrium on account of the absorption of water. In 

 most marine invertebrates death very quickly follows a transfer 

 into fresh water, that is, the limiting membranes are absolutely 

 permeable to water and osmotic diffusion is very rapid. (The 

 body fluids of all marine invertebrates, so far as known, are 

 isosmotic with sea water.) In Uca, on the other hand, the gill 

 membranes are apparently impermeable to water until the 

 strongly solvent power of the distilled water has attacked or 

 partially dissoved them and thus rendered them partially per- 

 meable. That they are eventually rendered permeable is shown 

 in the following experiments. A larger species of Uca ( U. minax) 

 was chosen because of its greater size, but the habits and reactions 

 of the two species are identical. The carapace of each crab 

 was cut away on both sides to expose the gills, and the gill cham- 

 ber was rinsed out. The carapace was then thoroughly dried 

 with absorbent cotton and the crab was carefully weighed, and 

 immersed in 200 c.c. of water distilled in Jena glass over potassium 

 dichromate and sulphuric acid. At intervals this water was 

 changed for a fresh amount and the sample titrated for chlorides 

 with potassium thiocyanate against silver nitrate, using iron 

 alum as an indicator. The following results were obtained : 



TABLE I. 



REMARKS. 



Crab No. I died shortly after 7 hours. 



Crab No. 2 died after 4 hrs., weighed immediately. Big claw cast at beginning, 

 wound seared with nitric acid. 



