. Journal of comparative neurology . 619 PLATE 2 EXPLANATION OF FIGURES 3 Reconstruction of Stage XVIII, age 100 hours; length 7 mm. shading andabbreviations as in figure 1. In the preauditory region a thickening has appearedbehind the epibranchial placode (horizontal shading). Since the placode ap-peared earlier than the thickening, it is called in the description of this regionthe posterior extension of the epibranchial placode, but it seems to be homologouswith the extensions behind the gill thickenings of the true gills with the excep-tion that they appear before the epibranchial placodes.

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. Journal of comparative neurology . 619 PLATE 2 EXPLANATION OF FIGURES 3 Reconstruction of Stage XVIII, age 100 hours; length 7 mm. shading andabbreviations as in figure 1. In the preauditory region a thickening has appearedbehind the epibranchial placode (horizontal shading). Since the placode ap-peared earlier than the thickening, it is called in the description of this regionthe posterior extension of the epibranchial placode, but it seems to be homologouswith the extensions behind the gill thickenings of the true gills with the excep-tion that they appear before the epibranchial placodes. The preauditory placodeis absent and the lateral line primordium is larger than in figure 2. In the post-auditory region the second ectodermal gill thickening is split at its anterior endinto two portions of which the more dorsal represents the posterior extension ofthe second gill and the more ventral the area of contact of the third gill. Theposterior portion of this second thickening is the angular thickening. 4 Reconstruction o

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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedicine, bookyear191