PLATE 5 



EXPLANATION OF FIGURES 



13 From 120^-hour embryo, shows the supra-orbital and sub-orbital lines at 

 the level of the Gasserian ganglion. X 300. 



14 Shows the detail of the posterior extension of the first gill thickening in 

 an embryo of 94 hours. X 300. 



15 From 120|-hour embryo, is taken four sections posterior to the section 

 shown in figure 13. The two lines are converging and the radial arrangement is 

 not so pronounced as in sections through more anterior points. X 300. 



16 From a 120|-hour embryo; shows the general relations of structures in the 

 region of the hyoid contact. This section shows the epibranchial placode, lying 

 just lateral to the hyoid contact and the primordium of the supra-orbital line, 

 situated dorsal to the epibranchial placode. The histological characters which 

 serve to distinguish the ectodermal thickening and the epibranchial placode from 

 the sensory line primordium are shown in this section. This section is five sec- 

 tions posterior to that shown in figure 15. X 300. 



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