CHAPTER LJi 



Interactions 



of Morphogenetic Units 



The process of orderly organization of the cortical net- 

 work of Podophrya parasitica which we have described is, 

 according to E. Faure-Fremiet.( 1945a), ''the transition be- 

 tween an amorphous state to an orderly state as if space 

 lattice forces have been responsible for a crystallization." 

 We do ^lot know yet whether the meshes of the parental 

 network disappear and are replaced by new structures or 

 are simply reshaped. The latter hypothesis seems to cor- 

 respond to the facts. Whatever the case may be, meshes 

 exist in the cortical network of the adult Podophrya, but 

 are differently arranged from those in the embryo. What 

 is the nature of the change? This is certainly an important 

 problem. 



The ciliate Sphenophrya dosiniae possesses a sucker 

 which undergoes a considerable development. The organ- 

 ism is apparently stretched by this rigid structure. In the 

 mature ciliate, the posterior ''pole," that is to say, the point 

 where the posterior ends of the kineties join, is located ap- 

 proximately on the middle of one "face." The cortical net- 

 work is very irregular. Some meshes are small and more or 

 less regularly penta- or hexagonal; some, especially in the 

 posterior region, are considerably longer, just as if the sur- 

 face had been stretched. These are indications of some 

 elasticity of the surface during the growth of the organism. 

 But if the meshes were just elastic, their size and shape 

 would be regularized after completion of the growth. This 



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