THE BILATERALITY OF APPENDAGES. 293 



In dealing with such a phenomenon it is necessary, to begin 

 with, to distinguish between facts of observation and any inter- 



Fig. 100. — Geometrical construction, including progressive " dorsiventrality " and 

 sliding-growth effect for system (8 + 13). Drawn with construction curve 

 (Type II. ) for uniformly retarded growth. ' / ^ 



pretations which may have been ascribed to them. Now the 

 facts observable are very definite: the rhomboidal primordia 

 apparently thrust laterally along their tangential diagonal, and as 



