Bulletin of the Museum of Comparative Zoology Volume 21

 
9781154077063: Bulletin of the Museum of Comparative Zoology Volume 21
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1891 Excerpt: ... ment, apparently unknown to Hoffmann, that the duct first appears in short fragments, each of which lies posterior to a segmental vesicle, could be readily brought into accord with these observations. In regard to the correctness of Hoffmann's conclusions that these evaginations represent a prouephros, I am of opinion that there is considerable room for doubt. The organ described by Hoffmann differs in two important respects from that of Selachii, and from the young stages of the Amphibian pronephros as presented in the first part of this paper. In the latter groups, while the metameric evaginations are yet continuous with the coelom, they have also fused distally to form a longitudinal canal (collecting trunk); this condition I wholly miss in Hoffmann's account, according to which all the evaginations remain distinct from each other till they have entirely separated from the coelom, and only the more posterior outgrowths ever fuse together. Secondly, no structure comparable to the Amphibian glomus is described. The latter objection would apply equally to the account given by Mihalkovics.1 None of the previous investigators were more successful in finding glomeruli of the pronephric type. In regard to the former feature, however, the account of Mihalkovics is more satisfactory, since the most anterior three pairs of vesicles stand in precisely this relation to the body cavity and to the collecting trunk (segmental duct). In reviewing Mihalkovics's interpretation, Hoffmann says ('89, p. 272), since " die Vorniere als eine Ausstiilpung, die Urniere nicht als solche entsteht, kommt es mir hochst wahrscheinlich vor, dass die Vermuthung von Mihalkovics, nach welcher die proximalen Urnierenkanalchen der Eidechsen der Vorniere der Amphibien entsprechen, eine ander...

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