124 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



twenty-four hours to greater variations at St. Andrew's than at Canso during em- 

 bryonic and larval life is the likely explanation. At St. A'ndrew's the extremes are 

 no doubt in April and August, but at Canso the range of variation is limited, and due 

 to the depth, &c., of the adjacent waters. The following chlorine determinations show 

 this : — 



Surface water, Canso, chlorine 1 '6543. 



Atlantic outside of Canso, chlorine, surface, 1-6032 ; 10 fathoms, 1*6302 ; 25 

 fathoms, 1-7262; 50 fathoms, 1-7476. 



The degree of salinity in the surrounding medium affects little the presence of 

 chlorine in medusse. If once a salt of sea-water is appropriated by the jelly, it remains 

 there for life, and any exchange must inevitably be slow. The jelly favours fixity and 

 uniformity of concentration, and the epithelium cells are effective as a barrier. Pro- 

 fessor Macallum's view is that heredity must be the cause of the selective power, 

 whereby the cells accept the lime and sodium salts on the whole as they are in sea- 

 water, and take in also the potash, but' reject some of the magnesium and sulphuric 

 acid. Whether, however, a power of choice was inherent from the first in medusae, or 

 developed as an acquired function, must be decided by the conditions regarded as 

 obtaining in their ancestral progenitors, and the sea-environment in which they existed 

 in past geological times. 



Coelenterates are a primitive type, indeed, the Graptolitidae of the Silurian 

 age, and the Silurian and Devonian Stromatoporida, are generally regarded by palaeon- 

 tologists as hydroids, and there can be no question of the remains of Jurassic medusae 

 in the Solenhaufen slates, and of at least one Cretaceous medusa ; and the reference of 

 these ancient forms to the order of (Craspedote) Trachymedusae, and to certain orders 

 of the Acraspeda, shews a striking stability in their morphological and structural! 

 features. 



What must have been the environment of the early jelly-fishes? What were the 

 surrounding conditions in the primitive seas which determined for these ancestral 

 Hydrozoans that fixity of inorganic composition referred to ? Professor Macallum 

 points out that the primal seas, when life first appeared, must have contained a less 

 quantity of salts, derived from the more readily decomposable rock materials, under 

 the enormous atmospheric pressures, and at the high temperatures, at which vapour 

 condensation first took place. 



Biologists are well aware of the fact that the simplest forms of animal life (such 

 as the Protozoan form Amoeba), while intolerant of extremes of heat, become sluggish 

 as the temperature rises above 15° C. until at 30° or 35° C. movements cease altogether, 

 but may be restored by lowering the temperature. If, however, the heat be raised to 

 40° C. heat rigour is produced, the protoplasm coagulates and the organism dies. There 

 is, of course, a certain percentage of salts in solution in the fresh watei in which 

 Amoeba lives. 



The sudden addition of 2 per cent of the chloride of sodium at once produces 

 dry-rigor and general shrinkage; but if the change be gradual Amoeba will live in a 

 4 per cent solution, i.e., one twice as strong as that which _results in dry-rigor, if the 

 change is sudden. Amoeba has no barrier-membrane or cellular layer, but merely an 

 ectosarc or slightly ditferentiated protoplasmic stratum externally. The contrast 

 between the Protozoa and the Metazoa renders deductions unsafe, but, after all. 

 Medusae are low in the scale. Experiments with a remarkable fresh-water Medusa 

 (Crapedacustas sowerhii Allm.*) discovered in the Eoyal Botanical Society's Gardens, 

 Eegents Park, London, some years ago, are interesting in this' connection. Marino 

 Coelenterates are not very tolerant of fresh-water, and the Medusa just mentioned is 

 the only non-marine jelly-fish known. Komanes found that it was even more in- 

 tolerant of change. Dropped ino sea- water at 85 °F. (being a tropical species) it 

 remained unaffected for 15 seconds, then there were two or three tonic spasms, lasting 



♦Professor Ray Lankester named it Limnocod'ium at the time of its discovery. See Nature, 

 VoL XXII., 1880 (pp. 147, 177, 361, &c.). 



