190 INITIATIVE IN EVOLUTION 



treacherous ground of inheritance amount to the very same con- 

 ception of personal selection and inheritance as are involved in the 

 term " educability " of Sir E. Ray Lankester. Whether or not 

 in the case of sponges this be a complete account of the matter it 

 at any rate is a very important piece of evidence, if valid, for 

 selection. Whether or not further it is a piece of evidence for a 

 Mendelian factor implicit in the primordial sponges and released 

 by some loss of inhibiting factors, as Professor Bateson would 

 probably claim, is another and far more imaginative conception. 

 The mere neo-Lamarckian with the aid of personal selection fails 

 to see any difficulty in realising the wonderful process described 

 by Professor Keith. 



An apology must be offered here to the patient reader for the 

 introduction under the heading of the " Evolution of a Bursa ' : 

 of the apparently alien subjects of bone-grafts, artificial new joints 

 and sponge-spicules, but I have hazarded the guess that all joints 

 in all animals have been fashioned — " forged by the incident of 

 use," to employ a fine phrase of Professor Macdonald's in another 

 connection — in slow but intelligible ways by use, and that in them, 

 as elsewhere, function has preceded structure. This arose so simply 

 out of the story of the bursse that I ventured to digress as aforesaid 

 rather than make it the subject of a separate section. 



The Significance of the Proceeding. 



The foregoing slender contribution to the comparative anatomy 

 and physiology of bursse is sufficient to show that at certain 

 important and " critical " points in the mammalian anatomy, 

 efficient bursse are always present. One cannot indeed conceive 

 the function of the parts involved being carried on at all without 

 these ingenious contrivances, and no doubt can exist that in certain 

 of the leading bursse selection guides and guards, while use and habit 

 maintain them. Over such as these " dominance " or the appear- 

 ance of mutations might perhaps be supposed to preside, and 

 possibly some useful statistical results might arise from their study 

 from these points of view. But, between these major bursse in 

 man and lower Primates and the undifferentiated sacs which hardly 

 deserve the name of bursse, there is a perfect little host of insignificant 

 structures, which at the first attempt at dominion over them on 

 the part of Mendel or de Vries would hoist the standard of revolt. 

 These would even refuse allegiance to Personal Selection under the 

 persuasive banner, " Educability," which however valuable else- 

 where, must stand aside in this little province of Nature. I have 

 thus attempted to " Lyell " this body of facts. Basing the state- 



