. Natural science: a monthly review of scientific progress. arrange-ment in Cladoselache). To recapitulate and discuss all the evidence for this theory wouldlead here into too many technicalities, and we must be content to 4^ NATURAL SCIENCE. Jan., regard it at present merely as a convenient guide for further investi-gation. The present writer is by no means convinced that it betterexplains the known facts than the theory to which he expressedadherence in 1892 (9). It is definitely known that among fringe-finned fishes the originally long lobate fin gradually become sshortened;and the abbrevia
. Natural science: a monthly review of scientific progress. arrange-ment in Cladoselache). To recapitulate and discuss all the evidence for this theory wouldlead here into too many technicalities, and we must be content to 4^ NATURAL SCIENCE. Jan., regard it at present merely as a convenient guide for further investi-gation. The present writer is by no means convinced that it betterexplains the known facts than the theory to which he expressedadherence in 1892 (9). It is definitely known that among fringe-finned fishes the originally long lobate fin gradually become sshortened;and the abbreviate lobate pectoral fin of the modern representativeof the order (Polyptevus) differs in no essential respects from thecorresponding fin of a typical modern shark. The facts of Palaeon-tology, as at present] understood, still seem rather to favour theidea that the same kind of evolution has taken place amongElasmobranchs. In conclusion, one word of protest against the American idea thatthe paired fins of Cladoselache (Fig. 2) can be compared with those of. Fig. 3.—Acanthodes bronni; outline restoration by Dr. A. Fritsch (4). LowerPermian, Germany. an Acanthodian (Fig. 3). We venture to maintain that these finsare fundamentally different in every respect. In Cladoselache the car-tilages of the internal skeleton are well developed and support thewhole fin-membrane; in Acanthodians, whatever view we may adoptas to the naming of the parts, these cartilages are as much reducedas in a modern herring. Dr. Dean (3) speaks of the radials ofCladoselache as if, by fusion, they might readily become a fin-spine likethat of the Acanthodian Parextts; but the former are cartilage andendoskeletal, the latter is merely the ordinary dentine and thereforepresumably exoskeletal. The problem of the primaeval sharkscontinues to present endless difficulties, but these are only multipliedby such comparisons. In the present writers opinion, the pectoral ofCladoselache is more remotely connected with th
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