PLATE 2 



EXPLANATION OF FIGURES 



6 4-min. Chelydra (13 segments). Sagittal" section somewhat further mediae! 

 than figure 5, passing through third head somite. X 175. 



7 Sagittal section through third head somite of a second embryo Chelj'dra 

 of 4 mm. X 135. 



8 4.5-mm. Chelydra. Transverse section through the forebrain and first 

 head somites. X 175. 



9 Section from same series, taken further anteriorly, passing through the 

 antero-dorsal wall of foregut. X 175. 



10 6-mm. Chelydra. Sagittal section through the mandibular arch, cutting 

 the outer edge of second head somite and the ventro-lateral diverticulum of first 

 head somite. X 175. 



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