110 MB. W. G. EIDEWOOD OlST THE HTOBEANCHIAL 



It has been brouglit about, not by the approximation of the 

 thyrohyals towards the median line, but by the forward migration 

 of the larynx over the hinder part of the hyobranchial skeleton. 

 The membranous space in the floor of the larynx in the adult 

 female (PI. 9. fig. 1) has evidently arisen by the absorption of 

 cartilage, for it is not represented in any of the young stages. 

 In this, as in the five preceding stages, the lungs exhibit the 

 accessory lobe on the mesial surface, which is such a distin- 

 guishing feature of the lungs of the adult Pipa. The bronchi 

 are still short, — a matter of some importance, since in Xenopus 

 the bronchus is nearly as long as the lung itself even in the 

 earliest stage. 



Parker includes, in his first stage of Fipa, embryos from the 

 dorsal pouches, of a total length of 9 lines, apportioned as fol- 

 lows : — head 2, body 3, tail 4. The external appearance of the 

 embryo (33. PI. 60. figs. 1 and 2) w^ould show that this stage is 

 earlier than my first stage, since the body is very small in pro- 

 portion to the size of the yolk-sac. But, judging by the figure of 

 the hyobranchial skeleton (33. PL 60. fig. 4), it should be later, 

 for both hyoidean and branchial plates are represented as less 

 expanded than in my Stage I. Parker figures the hyoid portion 

 of the hyobranchial skeleton as distiuct from the branchial, the 

 right and left halves of each portion being united across the 

 median line. These confusing characters render a more exact 

 correlation of the stages impossible. Parker's second stage — 

 ripe young, 6g to 7| lines in length, no tail — is older than my 

 Stage VI., and the hyobranchial skeleton does not difi"er materially 

 from that of the adult, except that the thyrohyal is unossified. 

 Parker states (p. 655) that the ceratohyal has disappeared, and 

 indicates by a dotted line the position which it should occupy ; 

 but, since he records no stage intermediate between that at which 

 the hyoid is " at its maximum " (p. 652) and that at which it has 

 entirely disappeared, he cannot be said to have unequivocally 

 proved the absorption. He mistakes the floor of the larynx for 

 an expansion of the hyobranchial cartilage and calls it the second 

 basibranchial ; and he fails to difi"erentiate the thyrohyal from the 

 laryngeal cartilage, although the two are readily separable at this 

 age. The ala of the adult hyobranchial skeleton he regards as a 

 derivative of the first and second branchial arches, the thyrohyal 



