Water 35 



in osmolar concentration to the abdominal body fluid, but salts are reabsorbed 

 from the urine aFter it enters the hind-gut. Similarly, in larvae of Lwinophilus 

 reared in a salinity equivalent to 0.01 per cent NaCl the osmotic concentra- 

 tion of the coelomic fluid was equivalent to 0.031-0.048 per cent NaCl, and 

 that of the secretion from the malphighian tubes was similar (0.031-0.066 

 per cent NaCl), whereas the rectal urine was verv dilute (equivalent to 0.000- 

 0.009 per cent NaCl). 44 



Sponges, Coelenterates, Flatworms, and Molluscs. I low fresh-water sponges 

 and coelenterates keep from swelling to the bursting point is not well known. 

 Fresh-water sponges appear to eliminate water by contractile vacuoles in 

 amoebocytes and choanocytes. Marine sponges lack these contractile vacu- 

 oles. '^^•* The osmotic concentration of cells of the freshwater sponge, 

 Spongilla, in summer is low (25-30 mM NaCl) but at the time of gcmmula- 

 tion the concentration rises (1 10 mM NaCl). -'••* 



Two fresh-water coelenterates (Pehnatohydra oUgactis and Chlorohydra 

 viridissima) have been maintained in brackish water of 0.25 per cent salinity, 

 where the cells were shrunken; in distilled water they were swollen. 



The endoderm cells of Hydra contain vacuoles which resemble the vacuoles 

 in the cells lining the gut of many turbellarians. These vacuoles in Hydra 

 are not seen to contract. When Hydra is placed in pyrex-distilled water these 

 vacuoles greatly enlarge; in a few hours the body cells separate and the animal 

 disintegrates. Addition of small amounts of salts (calcium and other ions) 

 to the distilled water does not prevent swelling and disintegration. Some sub- 

 stance must be present in pond water which keeps permeability to water low 

 and prevents separation of the cells. 



Free-living flatworms have an excretory system of protonephridia which 

 probably function in getting rid of osmotic water. In a culture of Stenostovnim 

 oedematus distended individuals were found to have damaged protoneph- 

 ridia. ^^^ A turbellarian, Gyratrix hermaphroditus, collected from fresh water 

 showed a well developed protonephridial system, parts of which took up 

 vital dyes. ^^7 In brackish-water specimens ampullae* and parancphrocytes 

 are absent; in marine specimens the tubules also are lacking. Pianaria •*•» and 

 Dendrocoelum ^ gain weight in distilled water and lose weight in physiolo- 

 gical saline, hence they must normally excrete a hypotonic urine. 



Fresh-water bivalve molluscs have a very low blood concentration. The 

 blood concentration goes up with increasing external concentration, but the 

 animals are unable to survive in concentrations which approach the concen- 

 tration of the blood of frogs and other fresh-water animals. "- Anodonta, 

 adapted first to distilled water and then transferred to dilutions of sea water, 

 showed no weight change in hypotonic solutions (less than A..=0.1) but lost 

 weight in more concentrated solutions. '"' Anesthetized specimens, however, 

 gained weight in a hvpotonic mcdium.^"^ Anodonta is, therefore, permeable 

 to water. Fluid from' the pericardial cavity passes through the nephrostome 

 into the kidnev. The blood and pericardial fluid arc equiAalcnt osmotically to 

 0.1 per cent NaCl and the urine to 0.06 per cent NaCl.-"' The blood is 

 under a hydrostatic pressure of about 6 cm. M,0, and the colloid osmotic 

 pressure of the blood is some 3.8 mm. H.O. This would allow the pericardial 

 fluid to be formed by filtration through the wall of the heart and P.ckcn - 

 actually drained pericardial fluid for a short time at the rate of 250-300 ml./24 



