. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. FROM TWELVE TO THIRTY-SIX SOMITES 169 â 'l: â -,;â . apex, so that by the stage of 29 somites the opening is reduced to a minute elHpse situated on the external side of the dorsalmost portion of the otocyst (see Fig. 93). This portion of the otocyst now begins to form a small conical elevation, and the final closure takes place on the external side of this elevation, which is destined to form the endolymphatic duct. The latter remains united to the epi- dermis at this point for a consid- erabl
. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. FROM TWELVE TO THIRTY-SIX SOMITES 169 â 'l: â -,;â . apex, so that by the stage of 29 somites the opening is reduced to a minute elHpse situated on the external side of the dorsalmost portion of the otocyst (see Fig. 93). This portion of the otocyst now begins to form a small conical elevation, and the final closure takes place on the external side of this elevation, which is destined to form the endolymphatic duct. The latter remains united to the epi- dermis at this point for a consid- erable period of time by a strand of cells which may preserve a lumen up to 104 hours (Fig. 98). The final point of closure of the oto- cyst is thus very definitely placed, and it coincides with the middle of the endolymphatic duct, that is, with the junction of the later formed saccus and ductus endolymphaticus. In the Selachia this duct remains in open communication with the exterior throughout life; the rela- tively long persistence of its con- nection with the epidermis in the chick may thus be interpreted as a Fig. 98. â Section of the otocyst phylogenic reminiscence of the an- of an embryo of 104 hours. The cestral condition. °^f ^^^ ^P^^^^.^f °^ "^^ ^^^'^^^ IS drawn out into a narrow ca- The Nose (Olfactory Pits). At ^^^ ^^.^ieh connects with the about the 28 s stage, the ectoderm endolymphatic duct (recessus on the sides of the head a short dis- labyrinthi). tance in front of the eyes appeals , a. Ball of cells in the otocyst . -^ \'~ (otohth?). b., Canal leadmg from thickened. 1 wo circular patches ot the surface to the otocyst. D. ectoderm are thus marked off, the end'l. Endolymphati^c duct D., Dorsal. Ect., Ectoderm of the beginning of the olfactory epithe- surface of the head. Gn., Audi- lium; at first this grades almost im- L Lateral. M., ., , . *, ... Median. V., ventral, perceptibly into the neighboring ectoderm. In the stages immediately
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Keywords: ., bookauthorlilliefrankrat, bookcentury1900, booksubjectembryology
