General principles of zoology . rgoes an enlargement,areas of the surface of the body, the ectoderm, becom-ing invaginated. Even in many caelemcrates and lowerivornis there arises an invagination at the anterior end ofthe cylindrical digestive tract, forming the ectodermalforegut or stomodceum (Fig. 55). From the higher wormsonwards, it is accompanied by a second invagination at thehinder end, the ectodermal end-gut, orproctodanni (); embryologically, this is formed as a blind sac whose,closed end is bounded by the likewise closed posteriorpart of the archenteron, now called also incscnt
General principles of zoology . rgoes an enlargement,areas of the surface of the body, the ectoderm, becom-ing invaginated. Even in many caelemcrates and lowerivornis there arises an invagination at the anterior end ofthe cylindrical digestive tract, forming the ectodermalforegut or stomodceum (Fig. 55). From the higher wormsonwards, it is accompanied by a second invagination at thehinder end, the ectodermal end-gut, orproctodanni (); embryologically, this is formed as a blind sac whose,closed end is bounded by the likewise closed posteriorpart of the archenteron, now called also incscntcron ormid-gut, until the separating wall disappears, whereuponmid- and end-gut communicate with each other, and thedigestive tract becomes a canal extending through theentire body. 126 GENERAL PRINCIPLES OF ZOOLOGY, Various Divisions and Appendages of the DigestiveTract.—The part which the archenteron takes in com-parison with the ectodermal proctodoeum and stomodoeumin making up the completed digestive tract is very differ-.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
