22 



Comparative Animal Physiology 



Even at equilibrium Maja forms 2 to 2.5 ml. of urine per hour, or the 

 equivalent of 3 per cent of its body weight in 24 hours. ^^ In dilute sea water 

 Maja becomes sluggish and its metabolism actually falls as its blood becomes 

 dilute. --- When the blood is isotonic with the medium the water excreted 

 cannot have entered osmotically and it is likely that water is actively absorbed 

 and excreted in the process of ionic regulation. -^^ 



Numerous other marine crabs behave similarly— Paiinwras vulgaris (Fig. 

 12),^- Portunas puher,^'^^^- ^^^ Portunas depurator (Fig. 10, curve E; Fig, 

 12), ^^^ Cancer antennarius, Lophopanopeiis heathii, ^peocarcinus calif orn- 

 iensis, ^-^ Hyas aranea (Fig. 12), '^^'^ and Pagurus longicarpus. ^"" When 

 Hyas aranea is put into a mixture of sea water and isotonic sugar, ^^^ there 

 is a brief rapid weight loss and then a slow rise in weight; thus salt is lost more 

 rapidly than sugar can enter. 



A, 



4 8 12 16 20 24 28 32 36 40 44 48 



HOURS IN DILUTE S.W. 



Fig. 10. Blood concentrations as freezing points (aO of several marine Crustacea after 

 transferring to dilute sea water at time 0. (A) Carcinus from Ao=2.33 to Ao=1.33. 

 (B) Carcinus from Ao=2.2 to A«=1.07. (C) Maja from Ao=2.2 to Ao=1.54. (D) 

 Maja from A..=2.33 to Ao=1.33. (E) Portunas from A"=2.1 to Ao=1.07. Data for 

 curves (A) and (D) from Schwabe;"- data for curves (B), (C), and (E) from Mar- 

 garia.^"** 



An interesting variant of an osmolabile crustacean is Lemaeocera hranch- 

 ialis, a copepod parasitic on codfish. The fish blood is hypotonic (equivalent 

 to 1.443 per cent sodium chloride), and while the copepod is attached to its 

 host it also is hypotonic to the sea water (equivalent to 2.0 to 2.8 per cent 

 sodium chloride), but when separated from the host it becomes isotonic with 

 the sea water (3.5 per cent saline). ^^- 



