ia8 HABITUDES AND ATTITUDES 



When both conditions and reactions in different 

 specific groups are identical, convergence based on 

 homology ensues. Thus the trophoblastic vesicle 

 of Peripatus nova-britannice is doubtless homo- 

 logous with that of the South African P. sedg- 

 wickii\ but the adaptation which produced the 

 structure out of the primitive matrix may have 

 been evolved independently, i.e., along closely 

 parallel lines in the two species. If this is so it 

 is an example of close specific convergence. 



In accordance with the Trophoblast Theory, the 

 trophoblast, wherever it occurs, is to be defined 

 as an outer larval, or extra-embryonic envelope 

 or appendage which has acquired phagocytic 

 properties in order to provide for the intra-uterine 

 nutrition of viviparous, terrestrial animals which 

 have descended from oviparous, aquatic ancestors. 

 In accordance with the theory of Larval Forms 

 amongst aquatic organisms other than Arthro- 

 poda, what may be termed by contrast the 

 kinetoblast or outer ciliated investment of the 

 larva has acquired special locomotor properties, 

 frequently concentrated along definite tracts, in 

 order to provide for the pelagic life and inde- 

 pendent nutrition of the young. 



From whatever point of view the matter may 

 be regarded, the parallelism between direct and 

 indirect development in Enteropneusta and 

 Onychophora, not to mention other cases, is a 

 very suggestive one. 



