. The development of the chick; an introduction to embryology . gins to form a small conicalelevation, and the final closure takesplace on the external side of thiselevation, which is destined toform the endolymphatic duct. Thelatter remains united to the epi-dermis at this point for a consid-erable period of time by a strandof cells which may preserve alumen 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 ofthe endolymphatic duct, that is,with the junction of the later formedsaccus and ductus endolymphaticus.
. The development of the chick; an introduction to embryology . gins to form a small conicalelevation, and the final closure takesplace on the external side of thiselevation, which is destined toform the endolymphatic duct. Thelatter remains united to the epi-dermis at this point for a consid-erable period of time by a strandof cells which may preserve alumen 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 ofthe endolymphatic duct, that is,with the junction of the later formedsaccus and ductus the Selachia this duct remainsin open communication with theexterior throughout life; the rela-tively long persistence of its con-nection with the epidermis in thechick may thus be interpreted as a Pig. 98. — Section of the otocystphylogenic reminiscence of the an- of an embryo of 104 hours. Thecestral condition. The Nose (Olfactory Pits). Atabout the 28 s stage, the ectodermon the sides of the head a short dis-tance in front of the eyes appearsthickenec. original opening of the otocystis drawn out into a narrow ca-nal which connects with theendolymphatic duct (recessuslabyrinthi).a., Ball of cells in the otocyst (otolith?), b., Canal leading from 1 wo circular patches of the surface to the otocyst. D. ectodenu are thus marked off, the end1. Endolymphatic duct. D., Dorsal. Ect., Ectoderm ot tliebegmnmg of the olfactory epithe- surface of the head, (in., Au<li-lium: at first this grades almost im- tory ganglion. L., Lateral. M., . - . Median. V., ventral, perceptibly into the neighboring ectoderm. In the stages immediately following the olfactoryplates appear to sink down towards the ventral surface of thehead, due no doubt to more rapid growth of the dorsal portionof the head. Thus they ajipear at the vent ro-lateral angles of 170 THE DEVELOPMENT OF THE CHICK the nnteiior part of tlic head at the stage of M^ somites. Durinf]^the disphicenient a depression appears in the
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