1908.] OF THE BATRACHIAN GEXUS HBMISUS. 929 



interior. The thickness of the walls is also shown in this 

 drawing. It is doubtless partly owing to the strong contraction 

 of the hearts at the moment of death. 



I am not aware that the posterior hearts of Xenopus have 

 been described. The pectoral lymph-hearts, howevei-, of this 

 Frog are described and figured by Dr. Bles in his beautifid 

 memoir* upon the larval development of Xenopus. There is but 

 a single pair, and each is enveloped in a lymph-sac of its own. 

 Dr. Bles remarks that the early development of these structures 

 in Xenopus is remarkable, since in Rana temporaria and Bufo 

 scalamita the author found that the pelvic lymph-hearts do not 

 appear until after the metamorphosis. This, however, does not 

 argue that these structures are new formations and not com- 

 parable with the lymph-hearts in Urodeles. It is hardly likely 

 that the anterior and posterior lymph-hearts are not parts of the 

 same series, and therefore the early development of the pectoral 

 hearts in Xenopus is to be set ofi" against the late appearance of 

 the pelvic hearts in certain Frogs, including, as it is to be supposed, 

 Xenopus itself. 



Inasmuch as the lymph-hearts of Hana are connected with 

 veins supplying the fore and hind limbs respectively, a suggestion 

 may be made as to the retention (or, if my opinion be not accepted, 

 the multiplication of these hearts) of three paii-s of posterior 

 lymph-hearts in Xe^wpios. While in most Frogs, indeed in all, the 

 hind limbs are the powerful swimming-organs of the animal, and 

 exceed in size the relatively feeble fore limbs, the disproportion 

 reaches its maximum in Xenopus. Of this Frog Dr. Bles justly 

 writes : — " The size of the arm is altogether out of proportion to 

 the size of the leg, which is an extremely powerful swimming- 

 organ. The limbs of Xenojnis as a Frog are paralleled by the 

 limbs of Macropus as a Marsupial " f. The excessive size of the 

 hind limbs in Xenopus bears some relation to the triple lymph- 

 hearts. It is true that I have not succeeded in finding the veins 

 into which the hearts open. But it can hardly be doubted, from 

 the position which they occupy, that their orifices are into veins 

 connected with the legs. 



Attention may be drawn to the variability of these posterior 

 lymph-hearts in Xenopus. This fact, as it appears to me, is of 

 itself evidence, though naturally not of a positive character, that 

 the structures in question are not a new formation, but are 

 derivatives of the chain of lymph-hearts in certain Urodeles. 

 The variability affects, as I think, the number of the hearts, 

 which does not only differ in individuals, but from side to side of 

 the same individual. But even if I am mistaken in this and 

 have simply failed to find the supposed missing hearts in those 

 specimens where only one or two appear to exist, there still 

 remains the variability in j)oint of size. There is, I hope, no 



■"• " Tlie Life-history of Xenopus Icevis Daud.," Trans. Ro}^ Soc. Eclinb. vol, xli. 

 pt. iii. 1905, p. 789. 



t Trans. Roy. Soc. Edinb. fom. cit p. 819. 



59* 



