. Carnegie Institution of Washington publication. DETAILS OF LATER EMBRYO. 103 the yolk as in the former specimen. A more detailed examination of this embrj'o shows that two gill-slits have broken through. The mouth, moreover, is more nearly completed, the mandible appearing and the visceral region having a more advanced contour. The pronephros is conspicuous. The pectoral fin is present as a longitud- inal dermal ridge. The tail, judging from its twisted condition, is evidently capable of active movements. This, however, in its detailed structure, as shown in a trans- parent preparation (plat
. Carnegie Institution of Washington publication. DETAILS OF LATER EMBRYO. 103 the yolk as in the former specimen. A more detailed examination of this embrj'o shows that two gill-slits have broken through. The mouth, moreover, is more nearly completed, the mandible appearing and the visceral region having a more advanced contour. The pronephros is conspicuous. The pectoral fin is present as a longitud- inal dermal ridge. The tail, judging from its twisted condition, is evidently capable of active movements. This, however, in its detailed structure, as shown in a trans- parent preparation (plate vni, fig. 46") is still distinctly immature; its tip retains a neurenteric canal («r), and a postanal gut {pag). In the latter the irregularity at the point x is probably artifact. The present embryo measured about 20 mm. in Fig. 78.—Transverse section passing through the posterior head region of embryo of plate VII, fig. 42. At the right the section traverses an auditory vesicle and the hyomandibular evagination. The latter fuses with the ectoderm, which here invaginates, but no opening has as yet been formed. Fig. 79.—Transverse section through the middle of the trunk region of the preceding embryo. df. Ectodermal anlage ot dorsal fin. P"- Pronephros. spc. Body cavity. hb. Hyomandibular evagination. ««• Subnotochordal rod. A third embryo of this stage is pictured in plate viii, fig. 49^ to ''. It measured about 35 mm. in length, and was observed living. It was this embryo whose capsule was taken accidentally on a trawl line during one of the writer's visits at Pacific Grove. As already noted, it was found developing in a creamy fluid. When placed in a watch-glass, its general position and color were as here repre- sented. It lay for a while on its side, its diminutive yolk-sac extending outward from the body and the delicate tail region showing constant undulatory movements. Most conspicuous were the bright-colored vessels on the yolk-sac, which
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