SKELETOIS" AND LARYNX OP XETSTOPUS AND PIPA. 95 



position, however, I fiad not a pair of cartilages, but a single 

 median piecs which shows signs of division into two only in the 

 third stage of development. This cartilage I take to be an 

 integral part of the mandibular arch — in fact, the median inferior 

 element or basimandibular. An examination of the first stao-e 

 especially shows that, although the inferior portions of the man- 

 dibular and hyoid arches are so dissimilar in size, they are built 

 essentially upon the same plan, and consist each of a pair of 

 eeratal elements and a median basal piece (see Plate 11. fio-. i). 

 In this respect the mandibular arch of Xenopus exhibits the 

 retention of a most primitive character. 



The above interpretation of the symphysial cartilage opens up 

 the question of the morphological value of mento-meckelians in 

 general ; and I am inclined to think that, in Anura at least, the 

 symphysial cartilages or bones are not labials developed, as the 

 upper labials undoubtedly are, in special relation with the 

 suctorial lips, but the modified right and left divisions of a 

 median basimandibular. The mouth of the young Pipa and 

 Xenopus is not suctorial, but has the form of a wide slit from 

 the very first ; and this fact it is which gives the young of 

 the Aglossa such a fish -like appearance. I have not been able 

 to satisfy myself concerning the presence of mento-meckelian 

 cartilages in Pipa. The mandible exhibits a symphysial segmen- 

 tation as early as Stage II. (fig. 5) ; and at Stage VI. (fig. 9) the 

 two rami are as distinct as in the adult. As already shown by 

 Parker (33. pp. 638, 651, and 655), no symphysial elements are to 

 be recognized in the adults of either Xenopus or Pipa. 



Stage I. (Plate 11. fig. 1.) Tadpoles ranging from those in 

 which the hind legs are just appearing, to those with the fore 

 legs recently extruded. 

 The branchial skeleton has attained its maximum larval deve- 

 lopment ; but it as yet shows no signs of absorption. On com- 

 paring the hyobranchial skeleton of Xenopus at this stage with 

 that of a more familiar anurous batrachian, e. g. Pana or Alytes, 

 one cannot fail to notice how small are the three branchial clefts 

 in proportion to the large expanse of the branchial cartilage. 

 Instead of four elongated bars of cartilage on each side, con- 

 nected distally by an epibranchial marginal bar, and confluent 

 proximally with a cartilaginous hypobranchial plate, we have 

 rather a pair of greatly inflated cartilages of considerable size, 



