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Show 1895.] MUSCULAR ANATOMY OF XENOPUS. 849 undoubtedly ally Xenopus more or less closely to Pipa. (1), (2), (7), and (8) are peculiar to Xenopus, and distinguish it from Pipa no less than from Rana. Nevertheless I have been able to point out in this paper a few new points of likeness between Xenopus and Pipa, of which the most important is, in m y opinion, the almost identical form of the " diaphragm " in the two genera, which has in both a musculature derived from three sources, instead of from only one as in Rana. The enormous latissimus dorsi, first described by Maurer, and the extension backwards of the abdominal musculature generally to overlap the thigh, is a strong approximation towards the actual attachment of these muscles to the femur itself in Pipa. These additional facts tend to justify the conclusion of Dr. Mivart1 and of Mr. Boulenger 2, not to mention others, that the two genera should be closely united in any scheme of classification, and perhaps to render this union even closer than has been suggested. O n the other hand, there is the question of convergence raised by Cope to be dealt with. That naturalist suggested some thirty years ago3 that Pipa may be to the edentulous Anura what Xenopus is to the toothed forms-that they are, in fact, the summits of their respective series. Dr. Mivart has already discussed the value of the characteristics known at the time when he wrote as evidence of genetic affinity. I shall not attempt any recapitulation, but shall deal here only with the new facts detailed in the present paper. It must be always borne in mind that both Pipa and Xenopus are among the most purely aquatic of Anurous Amphibia ; Xenopus is " essentially aquatic, the animal never leaving the water except in search of places where food or shelter are better supplied"4. The attachment therefore of the abdominal musculature to the thigh is perhaps more useful to a creature which is as a rule in a horizontal position in the water and which rarely, if ever, adopts the typical frog-like attitude upon the land. This particular resemblance, therefore, between Xenopus and Pipa may perhaps be regarded as of less importance than some others. W e next come to the lungs and their musculature, for the other myological resemblances between Xenopus and Pipa are mainly, if not entirely, related to the facts referred to in the foregoing paragraph. One cannot help suspecting that the muscles attached to the lungs render possible a more rapid aud thorough filling and emptying of the same with air-an advantage to aquatic though air-breathing animals. The great strength of the respiratory muscles in the whales5 is an analogy. The very differences between the lung-muscle of Xenopus and Pipa tend to support the i " On the Classification of the Anurous Batrachia," P. Z. S. 1869. 2 B. M . Catalogue of Batrachia Salientia. 3 Nat. Hist. Rev. 1865. 4 Leslie, " Notes on the Habits and Oviposition of Xenopus lavis," P. Z. S. 1890, p. 69. 5 Owen, Comp. Anat. vol. iii. p. 578. |
