PROGRESS OF LIFE. 598 



1. The fact of Progress. — The history with which the preceding 

 pages are occupied has presented the grand fact that the system of life 

 began in the simple sea-plant and the lower forms of animals, and 

 ended in Man. 



2. The progress in climate and other conditions involved a concurrent 

 progress from the inferior living species to the superior. — The existence 

 of a long marine era, through the Silurian and part of the Devonian 

 ages, admitted of the existence chiefly of marine life. Hence the domi- 

 nant type of the Silurian was the Molluscan, which, with the Radiate, 

 is eminently marine. In addition, there were marine Articulates and 

 marine Plants ; and, when the Vertebrates began, it was with marine 

 species, the Fishes. Thus the prevalence of waters involved inferiority 

 of species. The increase of land, the gradual purification of the 

 atmosphere, and the cooling of the globe, prepared the way for the 

 higher species. 



It is probable that the oceanic waters were also in an impure state, 

 compared with the present, from containing an excess of salts of lime ; 

 and this also involved the existing of inferior species, — such as Cri- 

 noids, Corals, and Mollusks, a very large proportion of whose weight 

 is in calcareous material. The removal of this excess of lime from the 

 waters produced limestone strata, purified the waters, and fitted the 

 oceans for other species. 



The great prevalence, in the Primordial, of Lingulce and some 

 related Brachiopods, having shells containing a large amount of phos- 

 phate of lime, is further evidence of the greater density of the waters, 

 and seems to indicate, as stated by Hunt, who first made known the fact, 

 the presence of an excess of phosphates. 



3. The progress in climate and in the condition of the atmosphere and 

 waters involved a localization of tribes in time, or chronographically, 

 just as they are now localized by climate over the earth's surface, or 

 geographically. — Living species are always adapted to some special 

 climate or condition of the globe ; and, when this climate or condition 

 had been passed in the earth's progress, the tribes fitted for it no longer 



and brought into the least compass consistent with the amount of brain. In the same 

 manner, the Carnivores, among the large Mammals (Megasthenes), are superior to the 

 Herbivores, the anterior limbs not having locomotion as their sole use, and the head 

 being more compacted and condensed, for the size of brain. The highest Crabs, the 

 Triangular, or Maioids, are superior in the same manner to the lower, and far more to 

 the Lobster tribe and other Macrourans ; descending in grade from the higher Crabs, the 

 outer mouth-organs become more and more separated from the mouth, and, finally, in 

 many Macrourans, they have the form of feet, thus passing from the head-series to the 

 foot-series. Insects are, on this principle, — that of Cephalization, as it is called by the 

 author, — superior as a class to Crustaceans, although of so much less size. 



Condensation anteriorly and abbreviation posteriorly is the law of all progress in em- 

 bryonic development, and also of relative rank among species of related groups. 

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