AUGUST 2, 1907] 



SCIENCE 



141 



As the ocean passed more and more de- 

 cidedly this optimum, the more vigorous 

 organisms resisted this change in various 

 ways. They cut themselves oif from it 

 osmotically. They secreted a more or less 

 impervious carapace or shell. Then they 

 got out of it entirely and migrated to the 

 air or the land, perhaps by way of the 

 shore sands and muds. This period when 

 the ocean seems to have passed its best 

 stage for life appears to have been the 

 Cambrian. After this period there was 

 a wealth of forms able to leave hard traces 

 of themselves. Before this period there 

 was no physiological need for skin or shell. 

 But once the skin and shell had been de- 

 veloped, primarily as a physiological reac- 

 tion against the water, their great advan- 

 tages for purposes of defense and support 

 no doubt soon made themselves felt. 



Before this the early dilute and perhaps 

 acid ocean water would attack shells freely. 

 After the Cambrian time there was an 

 excess of calcium carbonate, which has been 

 steadily thrown out, as the rivers brought 

 the carbon dioxide in, ever since. 



In passing I may say that Maeallum 

 has suggested that from the composition of 

 the protoplasm itself we may form some 

 idea of that of the early ocean, but as I 

 can not endorse his conclusions, I will not 

 dwell on them here. 



We thus attribute the development of 

 hard parts and a separate vital medium, 

 the one occurring at the beginning, and 

 the other at the end of the Cambrian, to 

 the same cause, the endeavor of the socie- 

 ties of cells we call organisms to maintain 

 for the mass of the constituent cells the 

 best possible conditions for their activity. 



We have thus, I conceive a fair explana- 

 tion for the rarity of traces of hard parts 

 in the early rocks. The animals had felt 

 no physiological need of them and had not 

 begun to develop them, and the ocean was 



relatively fresh, and would more easily 

 dissolve them. 



Moreover if the early ocean was chan- 

 ging in composition and growing more 

 favorable to cell life, while the organisms 

 were bathed in it, we might well expect a 

 rapid evolution, and one not merely super- 

 ficial. 



It is a standard doctrine of biology that 

 the individal in his growth gives a sketch 

 of the history of the race to which he 

 belongs, that embryology and phylogeny 

 run parallel. I do not know that any one 

 has heretofore suggested that the time 

 occupied in passing from one stage to the 

 corresponding stage is in any way pro- 

 portional in the two series, and that the 

 rapid changes in the egg at the beginning 

 are matched in racial history. It would 

 be indeed foolish to hold this in any rigid 

 way, for the parallelism is in no sense 

 strict. Yet is it not fair to suppose that 

 life as a whole was more plastic at the 

 start even as the individual is, and that as 

 in artificial races there is a cumulative 

 effect of heredity, tending to hold them 

 true after a few generations, so it must be 

 for organic life as a whole? 



As we have said, if we may estimate 

 by the concentration of the vital medium 

 relative to that of the pi-esent ocean, and 

 suppose the increase to have been uniform, 

 the time prior to the separation of a dis- 

 tinct body fluid, that is, the pre-Ordovician, 

 can be only a quarter of the time which has 

 elapsed since. A discussion of the tem- 

 peratures and change of ratios of sodium 

 to chlorine and magnesium to calcium, in 

 the present ocean and Paleozoic waters 

 while they do not agree closely, also lead 

 to the conclusion that the ocean at the be- 

 ginning of concentration by erosion was 

 only a fourth older than the early Paleo- 

 zoic ocean. 



This will give us room for all the sedi- 



