OSMOTIC AND IONIC REGULATION 235 



obviously promising material for the investigation of ion uptake. Koch 

 (1954) has found that many basic dyes, including methylene blue and 

 pyocyanine, are reversible inhibitors of salt absorption. These dyes con- 

 tain a quaternary NH4 group, and tetramethyl ammonium chloride is 

 also an inhibitor. Koch believes that the inhibitory action of basic dyes 

 is due to their anticholinesterase activity. Cholinesterase is present in the 

 blood of Eriocheir and very probably in the gill epithelium. The classical 

 inhibitor of cholinesterase, eserine (physostigmine), reversibly inhibits 

 the salt absorption in Eriocheir gills, and also the absorption of "Na by 

 the anal papillae of the midge Chironomus plumosus. 



Invertebrates which live and breed in fresh water have a wide range 

 in blood concentration. The lamellibranch Anodonta has a concentration 

 equivalent to about 4-5% sea water, A 0.08° C (Potts, 1954a), whereas 

 the crayfish Astacus has a concentration ten times as much, A 0.81° C 

 (SchoUes, 1933). In Astacus and Cambarns the urine produced by the 

 antennal glands has only about one-tenth the concentration of the blood 

 ( SchoUes,! 933 ; Lienemann, 1938), but in Anodonta and the gastropod 

 Lymnaea the urine is more concentrated, about 60% and 70% of the 

 blood concentrations, respectively (Picken, 1937). 



Eriocheir, on the other hand, produces urine isosmotic with the blood 

 at all dilutions of the external medium, and this is also true of the fresh- 

 water river crab Potamon edule. While Eriocheir is perhaps predomi- 

 nantly a brackish-water crab, young crabs penetrate hundreds of miles 

 up rivers, and the mature animals emigrate to the sea to breed (Krogh, 

 1939) . By its very active uptake of ions, this crab maintains a much higher 

 concentration of salts in its blood than Astacus, sustaining a A of 1.18° C 

 in fresh water, although freshly molted animals have a mean of 0.86° C, 

 27% lower. Potamon likewise has a high osmotic concentration in the 

 blood, A 1.17° C (Schlieper and Herrmann, 1930), but it is better adapted 

 to fresh water since it shows direct development, the young individuals 

 hatching from the eggs with all their appendages and becoming perfect 

 miniature crabs after one molt. 



The breeding of Eriocheir in the sea, and the fact that mature egg-bear- 

 ing females transferred to fresh water cannot survive more than a few- 

 days (SchoUes, 1933) emphasizes the fact that all stages must be capable 

 of living in fresh water for complete adaptation to this environment. In 

 Carcinus, the eggs from ovigerous females will develop normally only 

 within a salinity of 28-40 %o, although adults are found within 4-3 l%o in 

 the Zuiderzee and Den Helder areas (Broekhuysen, 1936), and there 

 must be other cases where the powers of osmoregulation of the adults are 

 not matched by those of their larvae. Another example is Mytilus califor- 

 nianus, which seems to show no regulation in diluted sea water. Gametes 



