618 Prof. Macallum. Inorganic Composition of the [June 23, 



elapsed since the Cambrian period. The Teleosts, as pointed out above, arose 

 in the Jurassic, and it is probable that the Gadidce have been marine since 

 the Cretaceous, yet in the blood of the cod the saline concentration is 1'2823 

 per cent, as against 1'7729 in the dog-fish. The difference, 0'49 per cent., 

 would seem to be attributable to the longer life which the Elasmobranchs 

 have undergone in the ocean, and it might be made the basis for determining 

 the relative length of the time which elapsed between the Cambrian and the 

 Cretaceous, could we with certainty know what was the original concentration 

 of the salts in the blood plasma in the Protovertebrates of the Cambrian or 

 Silurian. What it was we can only approximately conjecture. 



In the blood of mammals it is in the neighbourhood of 0"9 per cent.* The 

 difference between this and the 1'282 per cent, in the serum of the cod, 

 namely, 0"38 per cent., might be explained as caused by the action of the sea 

 water for all the time since the Cretaceous. On this basis the length of the 

 marine life of the Gadidce would be to the length of the marine life of the 

 Elasmobranchs as 0-38 is to 0-877. 



It is, however, not well to base any views on these data. For all the length of 

 time during which the Gadidce have been'associated with the ocean, the organic 

 solutes in their blood must be very minute in quantity. The A of the serum 

 and of its salts being respectively — 0'765° and — 0"7l°, the difference 

 ( — 0'055°) may be due to urea, ammonia salts, but even if due to urea alone 

 the amount must be very small. The ratio between 0'055° and 0'63°, the 

 A due to tlie urea in the dogfish blood, is very different from the ratio 

 O'SS : 0"877, and in consequence the latter cannot be regarded as indicating 

 the relative durations of the oceanic history of the Teleosts and Elasmo- 

 branchs. 



It may be that 0'9 per cent, is too low au estimate of the amount of salts 

 in the blood plasma of the ancestral type of Vertebrate, and that just as in 

 oceanic forms the growing saline concentration of the sea water tends and 

 has tended ever to increase, though slowly, the salts of the blood, so in 

 terrestrial forms the feeble salinity of their food and their environment may 

 possibly have in the long ages decreased the salts of the plasma considerably 

 below the ancestral standard. If the latter wore 1"2 per cent., the increases 

 in the salts of the serum in Teleosts and Elasmobranchs would be O'OS and 

 0'57, and this would give the relative durations of oceanic life in these classes 

 as 1 and 7. 



It is impoHsiljle, liowcver, to accept anything on tliis point as definite, and 



* Accordirifj to Btinge {lor. cit.) tho concon trillion of tlio Halts in liuinan blood serum is 

 0'842 -0"8fi7 per cent. Calculating from AhderliaUlon's analyses, tin; salts ot the sei uni 

 of tlio doj,' amount to 0 9.354, of tlio cat 0-9331, and of the sheep 0-9053 per cent. 



