10 t)R. W. G. EIDEWOOD ON THE [Jan. 18, 



The new gi'owth of cartilage (c) in front of the pointed lateral 

 process of the hypobranchial plate is larger in size and has assumed 

 a triangular shape. The thyrohyals are also larger and their 

 posterior extremities are dilated. The thyroid foramen does not 

 yet open, since the ceratobranchials, although separated from one 

 another at their distal ends, remain connected proximally. These 

 last remnants of the ceratobranchials are short and stunted, but, 

 seeing how near to the completion of their metamorphosis larvse 

 with tail reduced to a mere knob must be, it is surprising that any 

 branchial arches should be found at all. The first ceratobrauchial 

 is triangular in shape, but the other two are more rod-like. No 

 trace of the fourth is now to be seen. 



Stage 6. Specimen measuring 20 mm. from snout to cloaca. 

 Stump of tail 1 mm. Length of hind limb, extended, 23 mm. Length 

 of fore limb, extended, 11 mm. (Plate II. fig. 6.) 



The ceratohyals are more slender than in the previous stage, 

 and are of more uniform diameter throughout. They are thinnest 

 where they bound the hyoglossal sinus laterally. The sinus itself 

 is much wider than before, but not appreciably deeper. A couple 

 of slight notches in its border still serve to show how far the 

 ceratohyal cartilage is now situated from the median line. The 

 ceratobranchials have entirely gone, and the thyroid foramen has 

 opened out into a sinus. The thyrohyal (t) is thus formed by the 

 persistence and enlargement of that part of the hypobranchial 

 plate of the larva which forms the inner boundary of the thyroid 

 foramen. It is a matter of great satisfaction to me to be 

 able by the results of the present investigation to confirm the 

 view which I first propounded in the case of Pipa (8. p. 1U6), 

 and subsequently upheld in my paper on Pelodgtcs (9. p. 58(5). 



Since the first ceratobrauchial has in all the earlier stages been 

 distinguishable from the hypobranchial plate, and has now dis- 

 appeared, it is evident that it cannot form any part of the postero- 

 lateral process of the adult hyoid as it does in Pelodytes.^ It cannot 

 even be said that the pointed process of the hypobranchial cartilage 

 to which it was attached becomes the aforementioned process, 

 since this broadens out and fuses with the autogenous cartilage 

 marked c in fig. 6, and only differentiates into antero-lateral and 

 postero-lateral processes later. 



Stage 7. Completehj metamoiyhosed specim.en measunng 20 mm. 

 from snout to cloaca. No trace of tail. Length of hind limb, 

 extended, 23 mm. Length of fore limb, extended, 11 mm. (Plate II. 



Although the specimens which form the basis of the descriptions 

 of Stages 6 and 7 are hardly distinguishable by their external 

 characters, it is evident from the hyobranchial skeleton that the 

 one now under discussion is considerably the older. The cartilage 

 is much bluer, and more transparent and hyaline, than in the 

 preceding. The ossification of the thyrohyals is just beginning, a 

 small differentiated tract being discernible in the middle part of 



