. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. a. freigelegt wird" (p. 652) is a confirmation of the homology between this vessel and the excretory vessel of Ctenophores. Anything corresponding to the other excretory vessel of Ctenophores is not found in the grown Pohxlads, (where it would have to be sought for below the brain) but I-ang has found an indication of it in the early stages of development. The two accompanying diagrams, copied from Lang sliow these features clearly. The main axis given, the other plans are easily foim
. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. a. freigelegt wird" (p. 652) is a confirmation of the homology between this vessel and the excretory vessel of Ctenophores. Anything corresponding to the other excretory vessel of Ctenophores is not found in the grown Pohxlads, (where it would have to be sought for below the brain) but I-ang has found an indication of it in the early stages of development. The two accompanying diagrams, copied from Lang sliow these features clearly. The main axis given, the other plans are easily foimd. The excretory vessels lying ^^ always in the sagittal plane, it is accord- inglj' the longitudinal axis of the Polyclads which corresponds to the sagittal axis of Ctenophores, the transverse axis of the latter being then also transverse in Pol\- clads. From this then naturally follows tliat the nuchal tentacles of some primitive Polyclads (Planoceridse) are regarded as homologues of the tentacles of Ctenophores, being placed in the transverse plan. The gastrovascular system of Poly- clads and Ctenophores corresponds in seve- Fig. 10. Diagrammatic longitudinal section of a hypothetical ancestral ral important points. There is in both a form (a) and of a primitive form of Polyclads (Aiionymus) (b); the , , 1 , , ,T^i 1 former corresponds very nearlv to Cocloplana. br. places, where the large ectodermal pharvnx ("Pharyngeal- , , â \ , ,' j . n, ^ \, *' r . I ' J-. branching gastrovascular canals proceed from the stomach; excr. ex- tasche" in Pohxlads); to the "krausenfor- cretory vessel, in fig. b. the anterior branch of the gastrovascular .system; g. ganglion (apical organ); i. ni. inner mouth-opening; o. m. outer mouth- miger Pharynx" in the more primitive, opening; ph. phars-ugeal folds; ph. c. pharyngeal cavity; s sucking the "riissel" in more spezialized Polvclads, ^''^^- **â stomach (iufundibulum). 9 female genital opening. (Shghtly modifie
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Keywords: ., bookcentury1800, bookdecade1890, booksu, booksubjectarcticregions
