68 



INDIVIDUALITY IN ORGANISMS 



pharnyx, 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. 







«* 



^-.i^ 



13 



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

 stotnum girardi: Fig. 12, outline of adult worm, showing eyes, cephalic 

 ganglia, pharynx, and alimentary tract (after von Graff); Fig. 13, 

 longitudinal section near median plane of embryo, 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 pharnyx, 

 consist of numerous cells, and the morphological arrange- 

 ment is already apparent, while the whole postpharyn- 



