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A STUDY OF THE EVOLUTION OF THE AMPHIBIAN AND DIPNOAN PRONEPHROS BY AN ANALYSIS OF ITS RELATIONSHIP WITH THE ANTERIOR SPINAL NERVES
Author(s) -
FOX H.
Publication year - 1962
Publication title -
proceedings of the zoological society of london
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0370-2774
DOI - 10.1111/j.1469-7998.1962.tb05696.x
Subject(s) - caudata , anatomy , amphibian , biology , triturus , salamander , pronephros , salamandra , zoology , paleontology , genetics , xenopus , gene
The fact that an anterior spinal nerve and nephrostomial tubule and nephrostome are constantly associated with each other in individual specimens of urodeles, Anura and dipnoan larvae waa exploited to analyse the phylogeny of their pronephroi. Spinal nerves of numerically identical body segments but in different genera are homologous quantitatively i.e. develop from the same numbered segment as well as qualitatively; therefore it is assumed that individual but segmental pronephric units in different genera, when related to numerically identical spinal nerves, are homologous quantitatively and qualitatively also. A large number of nephrostomial units, e.g. present in the apodan Hypogeophis (Brauer, 1902) represents a primitive condition and commonly five functional units, though the fifth is reduced, are included in the pronephros of Cryptobranchus japonicus related to spinal nerves I to V (metotic segments 4 to 8; total body segments 7 to 11 inclusive). The phylogenetic development is expressed in the loss of front and rear tubules and can be traced through Hynobius retardatus, H. (Salamandrella) keyaerlingii, H. nebulosus, Necturus maculatus. Plethodon cinerevs and Ambystoma mexicanum to Triturus cristatus and Pleurodeles waltlii , which pronephroi each possess two functional nephrostomial units related to spinal nerves II and III (metotic segments 6 and 6; total body segments 8 and 9) or Salamandra maculosa and Desmognathus quadrimaculatus , where there are two units related to spinal nerves III and IV (metotic segments 6 and 7; total body segments 9 and 10). All the anuran pronephroi (except for a few which possess four units) originally are composed of three functional nephrostomid units related to spinal nerves I, II and III. If the anuran skull includes five segments (not counting the condyles) then the pronephric tubules belong to metotic segments 3, 4 and 6 or total body segments 6, 7 and 8; if the skull includes six segments the pronephric tubules would belong to metotic segments 4, 5 and 6 or total body segments 7, 8 and 9. Pronephroi of Neoceratodus and Protopterus— derived from a more numerous series of tubules (Kerr, 1919)—are each composed of two remaining funationel nephrostomial units, related to the nerves directly in front of the occipital and occipito‐spinal II arches (or their equivalent nerves in Protopterus ). This arrangement probably refers the tubules to total body segments 8 and 10 and thus functional tubules of body segments 7, 9 and 11 (present in Cryptobranchus japonicus ) are abaent. It is thought possible that the phylogenetic pattern described in the various specimens may provide a framework into which the pronephroi of all extant larvae of Urodela, Anura and Dipnoi can be arranged.