. Journal of morphology. latterlayer. Since Grooves I, II, III, etc. (see also Stage 14) are producedin regular order from before backward there is ground for sus-picion that they are intimately connected with the formation ofthe mesoblastic somites. In view of the fact that the segmenta-tion of the region immediately in front of Groove I is late in EMBRYOLOGY OF CRYPTOBRANCHUS 507 appearing and seldom clearly expressed (Stage 14), we must beon our guard against a possible discontinuity or difference inkind between the segmentation of the anterior and the posteriorregions of the cephalic plate
. Journal of morphology. latterlayer. Since Grooves I, II, III, etc. (see also Stage 14) are producedin regular order from before backward there is ground for sus-picion that they are intimately connected with the formation ofthe mesoblastic somites. In view of the fact that the segmenta-tion of the region immediately in front of Groove I is late in EMBRYOLOGY OF CRYPTOBRANCHUS 507 appearing and seldom clearly expressed (Stage 14), we must beon our guard against a possible discontinuity or difference inkind between the segmentation of the anterior and the posteriorregions of the cephalic plate. These points can be settled onlyby a careful study of sections of eggs that have first been describedexternally; but from surface views alone we are justified in claim-ing that we have in the open cephalic plate transverse divisionswhich may be homologized in different embryos, and which areprobably of true metameric value; hence they may be of use insolving the vexed problem of the segmentation of the Fig. 159 A. living embryo of Cryptobranchus allegheniensis in the early partof Stage 13, viewed in direct sunlight, and so far as possible by transmitted a freehand sketch of the upper hemisphere. X 10. A pair of depressions just within the neural folds near the ante-rior end of the cephalic plate probably indicate the anlage of theoptic vesicles (cf. Eycleshymer 95; Locy, 95). Some features of this stage are best brought out by the studyof living material; for-this purpose embryos have been examinedin direct sunlight. As shown in figure 159 a transverse opaqueband early appears directly in front of the neural plate in themedian region; in position and appearance it reminds one of theectamnion of the chick (Lillie 08, pp. 138 and 139). The neural 508 BERTRAM G. SMITH folds are conspicuous at an earlier stage in living than in preservedmaterial. In embryos later than the one figured, transversefurrows in the neural plate appear as described in preserv
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