1901.] NATURAL SCIENCES OF nilLADELPIirA. 249 



the pteiygo-palatiue bar (processus quadrate- cranial is anterior) 

 joins the quadrate, a very coaspicuous proliferation from the peri- 

 chondrium of the latter occurs. This proliferation forms a dense 

 strand of cells, which reach outward in the subcutaneous tissue 

 and aggregate themselves in a somewhat concentric fashion about 

 the distal, expanded termiuatiou of the Eustachian cord (Tym.). 

 The dense patch there formed is the Anlage of the future annu- 

 lar cartilage. From this region the Eustachian cord pursues the 

 same course that characterized the preceding stages. The cord 

 is, however, much more distinct than in any of the latter, and its 

 tubular character is plainly indicated by its nuclei, which are now 

 grouped about the periphery of the cord, thus giving the latter the 

 appearance of a duct with an obliterated lumen (PI. XI, fig. 29, 

 En.). In certain parts of the cord slight indications of a central 

 lumen can be made out, but, as a rule, any cavities that do appear 

 are neither very extensive nor pronounced. The cord, however, as 

 in the preceding stages, becomes smaller as it extends posteriorly 

 and in the region of the quadrato-hyoid articulation disappears. It 

 soon reappears, however. Posterior to the hyoid articulation the 

 cord again becomes much reduced, but does not lose its continuity 

 with the most posterior portion. In the most posterior part of its 

 course the cord again enlarges, becomes clearly tubular, and ex- 

 hibits a more or less well-defined lumen. In this portion the cord 

 occupies its characteristic position, ventral to the quadrate cartilage 

 and internal to the ramus hyomandibularis, which in the region of 

 the quadrato-hyoid articulation ascends from the ventral portion of 

 the hyoid arch to come into close relation with the outer wall of 

 the cord. From the dorsal wall of the " lateral recess " of the 

 pharynx a conspicuous strand of cells arises, the dorsal end of 

 Avhich closely approaches the Eustachian cord, but before actual 

 contact takes place the cord rather suddenly terminates. I am 

 not certain of the significance of this strand. It may be the part 

 which originally connected the cord with the pharynx, but of this 

 I am uncertain, since I found no evidence of it in stage VI. 



Stage IX. — Tadpole of 18 mm. Both fore and hind limbs 

 present. 



This stage marks the commencement of the metamorphosis. 

 Since the changes which the Eustachian cord (or tube) undergoes 

 during this period are obviously correlated with modifications 



