MORPHONS AND TROPISMS 169 



deep-seated, and intimate, more so than is 

 generally recognised. What may appear to be 

 a brilliant discovery of morphological affinity 

 may in reality be an equally brilliant demonstra- 

 tion of the no less important and interesting 

 phenomenon of morphological convergence ; the 

 closer the identity, as between forms belonging 

 to different phyla, the greater likelihood, or, as 

 I should prefer to say, the greater certainty that 

 it is due to convergence. 



What is known as homoplasy in morphology 

 might be called homotaxis in bionomics. In 

 contrast with the phenomenon of change of 

 function we have that of substitution of organs, 

 as Kleinenberg expressed it, or change of 

 morphon in Spengel's phraseology. Similarly, 

 in contrast with the Tropism Theory we must 

 have the Morphon Theory, and we must dis- 

 tinguish between primary or general morphons 

 which are, with due reserves, the intrinsic 

 property of all animals, and secondary or 

 phyletic morphons which are the special char- 

 acteristics of distinct groups. The relation of 

 morphons to tropisms lies at the basis of all 

 orthogenetic morphology and all convergent 

 morphology. Under the one or the other head- 

 ing all pertinent facts can be ranged, and none 

 need be left out of the reckoning. 



It will be observed that no attempt has been 

 made in the foregoing pages to formulate any laws 



