390 OUTLINES OF CHORDATE DEVELOPMENT 



a 



$i*&s&w ^sr^tofti:, t 



B 



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am 



FIG. 155. Sections through the blastodermic vesicle, or its embryonic portion, 

 of the bat, Vespertilio, showing the formation of the amnionic cavity. After Van 

 Beneden (Brachet). A. Section passing through the inner cell mass showing the 

 very beginning of the amnionic cavity. B. Amnionic cavity clearly indicated as 

 irregular spaces. The endoderm is torn away from its normal position under 

 the embryonic ectoderm. C. Thickened trophoblast now a syncytiotrophoblast. 

 D. Amnionic cavity fully established. The endoderm is torn away from the 

 wall of the vesicle at its ends, a, Amnionic cavity; am, amnion; b, capillaries of 

 the uterine wall; c, embryonic ectoderm; e, endoderm; i, inner cell mass; s, 

 syncytiotrophoblast; t, trophoblast; v, cavity of blastodermic vesicle. 



