68 



INDIVIDUALITY IN ORGANISMS 



pharynx, and alimentary tract; Fig. 13 is a longitudinal 

 section, almost in the median plane, of an embryo of the 

 same species. The anterior end is toward the left. 



■■^:'^^ 





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Figs. 12, 13. — Axial developmental gradients in flatworm, Plagio- 

 stomitm giradi: Fig. 12, outline of adiJt worm, showing eyes, cephalic 

 ganglia, pharj^nx, and alimentary tract (after von Graff); Fig. 13, 

 longitudinal section near median plane of embr>'o, head at left, showing 

 the apico-basal or longitudinal and ventro-dorsal gradients in rate of 

 development (from Bresslau). 



The organs of the anterior end, the brain and pharynx, 

 consist of nmnerous cells, and the morphological arrange- 

 ment is already apparent, while the whole postpharyn- 



