vi AGLOSSA 145 



from the anterior end of the ilia and spreads out fan-like to 

 the oesophagus and to the bases of the lungs. 1 This diaphrag- 

 matic arrangement is correlated with the great development of 

 the lungs, and is not a primitive but an advanced feature. It is 

 reasonable to suppose that this has caused the reduction of the 

 usual arteria pulmo-cutanea, and that the other two cutaneous 

 arteries have been developed secondarily. The Aglossa are 

 generally considered as the lowest Anura, and only Cope looked 

 upon Pipa and Xenopus as two convergent terminal branches. 

 Beddard came to the conclusion that both are closely related to 

 each other, chiefly on account of their peculiar diaphragmatic 

 arrangement. The whole question has entered upon a new stage 

 since the recent discovery of Hymenochirus, which is in many 

 ways intermediate between the two other genera. Moreover, the 

 mid-Tertiary Palaeobatraclms of Europe is undoubtedly related to 

 them, and we conclude now that all these four genera belong to 

 one group with a distribution formerly much wider than Africa 

 and part of South America. But this does not necessarily mean 

 that the Aglossa are in all respects the most primitive group 

 of living Anura. On the contrary, they possess few decidedly 

 primitive characters, namely, the long typical ribs, the presence 

 of the first spinal nerve, the unimportant persistence of the 

 arteria sacralis, and lastly, the possession in the tadpoles of a 

 right and left opercular " spiracle." The absence of the tongue 

 cannot possibly be an archaic feature, considering its universal 

 presence in all the other Amphibia, including the Apoda, and 

 the suggestive circumstance that this organ is least developed in 

 the entirely aquatic members of the Urodela. In fact, thoroughly 

 aquatic creatures, which seize and swallow their prey under water, 

 require no elaborate tongue ; and since we know that the Anura 

 must owe their typical formation to terrestrial life, it follows that 

 those which have again taken to the water and are tongueless, 

 have lost this organ. As I have shown elsewhere, 2 the epichordal 

 development of the vertebrae is likewise a secondary feature, far 

 from primitive; and the tendency of the shortening of the 

 vertebral column, which has reached its extreme in Hymeno- 

 chirus, points to the same conclusion. The apparatus of the 

 shoulder-girdle and sternum is in the last transitional stage from 

 the former arciferous to the typically consolidated firmisternal 



1 Beddard, P.Z.S. 1895, p. 841. 2 Phil. Trans. B. 136, 1896, p. 1. 



VOL. VIII L 



