PLATE 3 



EXPLANATION OF FIGURES 



5 Reconstruction of Stage XXI; age 120| hours; length 8.5 mm.; shading and 

 abbreviations as in figure 1. In this stage the supra-orbital, infra-orbital and 

 mandibular lines have grown forward almost to the optic vesicle. The epibran- 

 chial placode has reached nearly its maximum size and projects into the meso- 

 derm, but its point of attachment is not shown in this plot. In the postauditory 

 region there are three lateral line primordia, one over the first gill, one over the 

 second gill thickening and a third beginning over the third gill thickening and ex- 

 tending back from this point. The last is the primordium of the main lateral 

 line. There are four gill thickenings, the first three extending behind the first 

 three gills and the fourth lying in the region of contact of the fourth endodermic 

 gill pocket. 



6 Reconstruction of the preauditory region of Stage XXVI; age 154 hours; 

 length 10 mm. The extent of the preauditory lines at this age is shown, as well 

 as the persistence of the hyoid ectodermal thickening. 



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