THE WONDER OF LIFE 621 



become like a gizzard, with thick and muscular walls. 

 This is associated with a unique reduction of the front 

 of the breast-bone, and a consequent lessening of the 

 area for the attachment of the muscles of flight. 



%' v^^r^if^ 





Fig. 98. — ^New Zealand Lizard, Sphenodon or Hatteria, an archaic 

 reptilian type, sole survivor of the ancient race of RhynchocephaUa. 

 (From a, specimen.) 



Conservation in Evolution. — We wish to expand the 

 idea of the Uving past into a general conception of the 

 conservative tendency in evolution. There is, it seems to 

 us, a very hteral sense in which we may think of the higher 

 animals as heirs of all the ages. Particularly effective 

 modes of vital behaviour, some of which made a fortune 

 in their day, yet did not save their possessors from utter 

 ruin, have been caught up by collateral relatives and 

 handed on as a legacy from by-gone ages to the higher 

 animals. Where, for instance, would a higher animal 

 be — ^what possibiUty of such a Ufe would there be — ^without 

 a persistence of that most primitive manifestation of hfe 

 which we call amcfiboid movement — ^the ebb and flow 

 of a protoplasmic tide — so famihar to students of biology 

 in amoebae and white blood corpuscles ? How long would 

 a higher animal survive without its body-guard of phago- 

 cytes ? Nor could it have become what it is, had not its 

 embryonic nerve-cells flowed out into nerve-fibres, just like 

 exploring Amoebae ! 



