102 



ME. W, a. EIDEWOOD ON" THE HTOBRA]S"CHIAL 



Pipa americana. 



Here, as in Xenopus, the mode of development of the hyo- 

 branchial skeleton is practically unknown. Parker kas con- 

 tributed a certain amount of information*, but beyond this tke 

 subject has not been touched. Grronberg (18. p. 635) speaks of 

 having discovered in the larva of Pipa that, as in the adult 

 female, the isthmus between the anterior and the posterior parts 

 of the basal plate is a continuous cartilage, but he gives no 

 further information, nor any figures of larval structures. The 

 specimens available for this part of the investigation were suffi- 

 ciently plentiful to render it possible to obtain much more 

 complete and satisfactory results than was the case with 

 Xenopus. For many of the specimens I am indebted to the 

 kindness of Prof. Gr. B. Howes ; the remainder were obtained 

 by purchase from Y. Pric of Prague. 



It will be found convenient to choose six stages of develop- 

 ment for description here. There is more uniformity in the size 

 of embryos of the same age than in Xenopus, since the young of 



Embryos of Pipa. 

 Measurements in millimetres. 





From snout 



to root of 



tail. 



Length 

 of tail. 



Length of 

 extended 

 hind limb. 



Length of 

 extended 

 fore limb. 



Stage I 



10 



12 



11-5 



13 



12 



11 

 11-5 

 9 

 12 



11 

 11 



14 



13-5 



15 



13 



14 



12 

 11 



6-5 



8-5 

 10 



9 

 10 

 10 



6 



9 



9-5 





 

 

 3 

 



4 

 6 



7-5 



7 

 7 



7-5 

 7 

 8 

 7-5 



9 

 10 



10 

 11 

 11 

 10 

 10-5 





 3 



5 



5 

 5 



4-5 

 4-5 

 4-5 

 4-5 



5 

 5 



5-5 



5-5 



8 



6 



5-5 



Stage II 



Stage III 



Stage IV 



Stage V 



Stage VI 





* For a criticism of which, see p. 110. 



