1895.] MTJSCTTLAB AWATOMT OF XEKOPUS. 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 Kana. 



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 my 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 Pipia. These 

 additional facts tend to justify the conclusion of Dr. Mivart ^ and 

 of Mr. Boulenger ^, 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. 



On the other hand, there is the question of convergence raised by 

 Cope to be dealt with. That naturalist suggested some thirty 

 years ago^ 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"*. 



The attachment therefore of the abdominal m.usculature 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. 



We next come to the lungs and their musculature, for the other 

 myological resemblances between Xenopus and Pij)a 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 and 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 whales " is an analogy. The very differences 

 between the lung-muscle of Xenopus and Pip)a tend to support the 



1 " On the Classification of the Anurous Batracbia," P. Z. S. 1869. 

 " B. M. Catalogue of Batrachia Salientia. 

 3 Nat. Hist. Eev. 1865. 



* Leslie, "' Notes on the Habits and Oviposition of Xenopus Itsvis," P. Z. S. 

 1890, p. 69. 

 ° Owen, Oomp. Anat. vol. iii. p. 578. 



