. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. XOTES. '75 metry, and the recent researches of E. B. Wilson and Lwokf lead to the conclusion that the so-called mesohlastic pole-cells, which were described by Hatschek, have no real independent existence. 3. (p. 123.) Whether the dorsal and ventral fin-spaces are actually derived from the original myoccjul, as described by Hat- schek, or do not rather arise by a splitting of an originally solid thickening of the gelatinous connective tissue which sur
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. XOTES. '75 metry, and the recent researches of E. B. Wilson and Lwokf lead to the conclusion that the so-called mesohlastic pole-cells, which were described by Hatschek, have no real independent existence. 3. (p. 123.) Whether the dorsal and ventral fin-spaces are actually derived from the original myoccjul, as described by Hat- schek, or do not rather arise by a splitting of an originally solid thickening of the gelatinous connective tissue which surrounds them, must remain doubtful. The cavity of the metapleural folils certainly arises as a schizoca'l, by a hollowing out of a solid thickening. Even in case the fin-spaces also arise as schizoc(cIs, Hatschck's interpretation of their morphological significance might still hold good. 4. (p. 123.) A transitory pouch-like diverticulum of the myo- cccl has been observed in connexion with the formation of the sclerotome in the Selachian embryo by Rahl and H. E. 5. (p. 129.) Since the work of Balfour on the development of Elasmobranch fishes (Selachians), it has been known that the paired priemandibular head-cavities comrnunicate with one another across the median line in the embryo. The imi)ortant results obtained by the researches of Kupfffr (Fetromyzon, Acii)enser), Kasi'schf-NKO (Selachian), and Julia (Selachian), not only established the fact that the praimandibular cavities arose essen- tially as anterior archenteric pouches (cf. Fig. 72), but also that the median cavity which effected their communication across die middle line, from side to side, arose by constriction from the front end of the archenteron (using the latter term with some latitude), and that, therefore, the laiiofi of the right and left pranuDuiibular cavities in the embryo of the craniate Vertebrates is primary, and not secondary, as was previously supposed. I'or an excellent hist
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
