(614 Prof. Macallum. Inorganic Composition of the [June 23, 



In the blood of the lobster the ratios, though they are on the whole 

 parallel to those of sea water, differ from the latter, particularly in regard to 

 the SO3 and the magnesium. These are toxic constituents in sea water, and 

 though ' in Limulus, because of its association since remote geological time 

 with the ocean, a considerable degree of tolerance for them has been estab- 

 lished, only a very limited adjustment to them has been developed in the 

 lobster, whose marine history can l)e traced as far back as the Jurassic 

 period only, that is to a far less remote period than in the case of Limtdus. 

 The ancestors of the Homaridce are supposed to have been fresh-water forms 

 of an astacoid character and a species of Astacus, A. vedens, is found in the 

 so-called Lobster Beds in the Greensands of the Isle of Wight, belonging to 

 the Cretaceous period. In the earlier period, the Jurassic, the macrouran 

 decapods arose and their remains are found in deposits formed in more or 

 less still waters, such as the Solenhofen slates, in which they are mingled 

 with terrestrial and fresh-water forms. This suggests that the Mesozoic 

 ancestor of the lobster of to-day must either have been of a fresh- water 

 type or one that resorted to embayments, lagoons, or stretches of water more 

 or less surrounded by land, and therefore of a fresh or slightly brackish 

 character. 



It is to be noted, further, that in the blood of the lobster the percentages 

 of sodium and chlorine are 0"9033 and 1"547, while in Zinuthis they are 

 0'8885 and 1"6608. As the sea water at St. Andrews, New Brunswick, 

 in April and August yielded on analysis 0-7423 and 0'9882 per cent, of 

 sodium and 1'347 and 17473 per cent, of chlorine the sodium and chlorine 

 concentrations in the blood of the lobster probably are approximately the 

 mean values for the sodium and chlorine of its liabitat. From this it would 

 appear as if the sodium chloride of sea water passes freely into the blood till 

 the sodium chloride concentration in both is approximately balanced. 



In tlie serum of the dogfish, cod, and pollock the total salts are mucli less 

 than in sea water. In the dogfisli they are 1'7739 per cent., while in the 

 cod|and pollock they are 1"2823 and 1-2934 per cent, respectively. This 

 marked difference is undoul)todly due to tlie difl'erence in the length of time 

 in which tlie Elasmobranclis and Teleosts have been associated with the 

 ocean. The former have always been marine* since their oi'igin in tlie 

 Silurian period, while the Teleosts date only from the .Jurassic and wore 

 probably derived from an A)iiia-\i]<.e (Janoid. The Ganoids were abundant 

 in I'alitozoic and Mesozoic Seas, but these were probably also fresh-wator 

 forms, although through the scantiness of fresh-water deposits no evidence 

 of Kiicli is known. The ])re8ent day Ganoids, iiKjliidhig Amia, are all frcsli- 

 * A .sliJii-k, < 'arc/iariuK vicaragvfnKin, is native of tlio fre.sli-water Lake Niciiragua. 



