122 ME. "W. G-. EIDEWOOD ON THE HTOBEANCHIAL 



to suppression, of the larval development in Pipa is of course 

 directly related to the protected position wliich the embryos occupy 

 on the back of the mother, Tbe paired spiracular aperture of 

 Xenojpus larvae is a primitive character, and the absence of a sucto- 

 rial mouth with horny teeth shows less specialization than in 

 more familiar tadpoles. The absence in Pipa and Xenopus of a 

 persistent pre-renal part of the embryonic post-cardinal vein, 

 which persists so frequently in the Discoglossidae (22), is a sign 

 of extensive departure from the primitive type. The epipubic 

 cartilage of TJrodela is represented in Xenopus by the racket- 

 shaped cartilage in the postero-ventral body-wall ; but it is not, 

 so far as I am aware, found in any other Anura. It is not pre- 

 sent in Pipa. In the retention also, by the adult, of the organs 

 of the lateral line, and in the possession of claws on the first three 

 digits of the hind foot, Xenopus is unique among Anura *. 



In the characters of the shoulder-girdle, the genera Pipa and 

 Xenopus would appear to be more closely allied to one another 

 than to any of the Phaneroglossa t ; and the characters of the 

 muscular system recounted by Beddard, taken in conjunction 

 with the anatomy of the hyobranchial apparatus set forth ia the 

 body of the present paper, and the features of the carpus and 

 tarsus, tend in the main to show that, however much at 

 variance they may be in many details of anatomical structure, 

 the two genera, Pipa and Xenopus, have a true genetic relatiou- 

 ship, and are not to be looked upon as the culminating members 

 of parallel series. The suggestion of convergence put forward by 

 Cope cannot yet be considered as finally disposed of, but the most 

 recent evidence that has been brought to bear upon the question 

 points towards a common ancestry of the two tongueless toads. 



List oe Atjthoeities eefeeeed to. 

 1. Beddard, F. E. — " On some Points in the Anatomy of Pipa 

 americana:' Proc. Zool. Soc. 1895, pp. 827-841. Five 

 figures in the text. 



* Since writing the above, Mr. Gr. A. Boulenger, F.R.S., has been good 

 enough to demonstrate to me the presence of a persistent lateral line in Lepto- 

 brachium monticola, Rana hexadactyla, and various species of Pseudis, and has 

 furnished me with a reference to his published allusion to the fact : — Ann. Mus, 

 Genova (2), xiii. 1893, p. 344. 



t Cope, however, states (6. p. 98) that the Aglossal sternum finds a close 

 parallel in the Rhinophrynidaa. 



