7i6 LIFE : OUTLINES OF GENERAL BIOLOGY 



and far, even his most visionary simplifications fiad in them the 

 suggestive values of vision. 



His essential theorising has indeed been yet more boldly applied 

 to the interpretation of racial evolution, as notably by the American 

 palaeontologists, from Hyatt onwards. Viewing the course of indivi- 

 dual life as not only from embryonic to adolescent and adult phases, 

 but beyond this to senescence and death, they have applied this in 

 careful detail to the history of species, genera, and families, as 

 notably through the rich series of well-preserved shells of cephalo- 

 pods and other molluscs. They have first traced out the series, from 

 straight belemnites, through bent and curved forms, to loose- 

 coiled and thence to close-coiled forms like Nautilus ; and they have 

 shown that this evolutionary series is corroborated in the actual 

 development of some fossils. They next trace a similar series amongst 

 fossil Ammonites, which go farther in their complications, such as 

 the partitions so remarkably developed between successive chambers. 

 They interpret these, and also the external elaborations of shell- 

 markings, etc., as indications not only as so far in progressive series, 

 but next as reaching to exaggeration beyond utility; and all this 

 they associate with the decline and approaching extinction of the 

 species, no less than with that of the individual. In other forms, 

 again, they find regressions in shell-forms after the acme of their 

 progress, and towards simplification of coiling and other com- 

 plexities; and this they interpret as senescence carried on into 

 senilescence, and thus towards extinction of the race as well as the 

 individual death. It is a speculation familiar as far back as our 

 biologic memories go, that the great Irish deer, with his vast spread 

 of antlers, exaggerated in weight even beyond the strength of the 

 big skeleton, died out from over-specialisation ; and so for the sabre- 

 toothed tiger, whose immense canines seem to have outgrown their 

 purpose; and again for various elephantine types, surely over- 

 tusked, to magnificent uselessness. Such views, then, are well worth 

 considering, and they seem to be gaining ground: thus one of our 

 most experienced palaeontologists, Smith Woodward, interprets the 

 giantism in which so many groups have culminated, like so many 

 reptiles of the past, or whales and elephants to-day, as a sign of 

 their approaching decline; but here surely for obvious reasons, as 

 of great consumption of food threatening to pass beyond supplies, 

 of slower maturity and of lessened rate of reproduction rather than 

 from senescence proper. A more distinctly senescent character seems 

 that of the thickened and spiny shells of many molluscs, the stony 

 armour of many crabs as compared with lobsters, or the exaggera- 

 tion of coat-armour in so many extinct fishes, reptiles, and more. 



Degeneracy, too, has often been associated with specific and 

 individual senescence. Yet loss of teeth, as by birds, has been turned 

 to varied evolutionary purpose. And among mammals, the toothless 



