INTERACTIONS OF MORPHOOENETIC UNITS 79 



is not the case. Things happen as if "tension forces" were 

 acting continuously, or as if meshes, extensible during de- 

 velopment, had turned into a rigid structure after the max- 

 imal size was reached. 





f:-i/^'V^i^ 











^i •: •' J' * •'■•■ • ■■ • .*'; 



'^/H' :■■:.: •■*■■. 





•^// ^•;7■■.•^*t;■/'••y^y 



.'•V^.' 





Fig. 31. Sphenophnja dosiniae. The meshes of the cortical network 



are very elono;ate(l in the vicinity of the posterior region (between 



the V formed by the posterior sectors of the cihary system). 



