178 SYMBIOSIS 



applications but such stimulations attended as they are by 

 losses of other, milder, yet more vital stimulations, are followed 

 by sudden and often startling exhaustion of the species. The 

 balance of the account in the end shows a loss. Something of 

 the sort has happened to the birds as a class, for we are told : 



Si rapide a ete leur evolution que, dans les couches m ernes oii disparaissent 

 sans retour, les derniers Pterosauriens, les Pteranodontit6s, on rencontre 

 des Oiseaux tenement differencies que certains d'entre eux, tel Hesperornis 

 regalis, Marsh, en avaient deja perdu la faculte de voler. 



To say that the heavy, flightless, and wingless Hesperornis 

 was highly differentiated, is putting rather a peculiar complexion 

 on the case. We need to know the physiological reason for the 

 degeneration of the bird, and the reason is this : in-feeding together 

 with its anatomical correlations, leading to inferior adaptations. 

 In bio-economic terms, the bird had become divorced from the 

 leading (symbiotic) adaptation of its order and had to pay the 

 penalty by losses in many directions. As I have emphasised in 

 my Evolution by Co-operation, the bird was a gigantic 

 diver, allied to the grebes of to-day. The set-back of the legs, 

 and the large knee-cap and enemial crest seem to have rendered 

 an erect position impossible. The explanation of the Anatomy 

 of the bird is to be found in its feeding habits. 



As Ch. Deperet surmised, the rapidity of evolution of a group 

 is in inverse ratio to its longevity. He should have added that 

 longevity depends in the first place upon cross-feeding. The 

 class of the birds includes many excellent examples showing 

 that cross-feeding species excel in longevity. 



Of the Ratitae, the name applied by Huxley to the order of 

 flightless birds of old, in which the sternum is destitute of the 

 prominent ridge or keel, to which the large pectoral muscles are 

 attached, we are told that " leur inadaptation au vol ' par defaut 

 d'usage' entraine leur Degenerescence," and we get an allusioi 

 to Owen's remark that Nature presents no greater anomaly thai 

 a bird which cannot fly. " Get oiseau dechu, c'est le Ratite." 

 But, surely, we have here " misuse," over and above " disuse," 

 and it is not enough merely to continue " Mais qui dit Anomalie, 

 dit le plus sou vent Degenerescence." Instead we should 

 shown that the transformations, or "mutations," based upoi 

 in-feeding, never have the sanction of Nature, and that onl\ 

 cross-feeding can provide the physiological groundwork fit for 

 abiding transformations. 



