2'52 PROCEEDINGS OF THE ACADEMY OF [March, 



as in a number of other stages, a ciitlerence in the coudiliou of the 

 tubes of the two sides. Posteriorly the tube terminates without 

 forming any connection with the phax'ynx. The proliferation 

 from the pharynx is not very distinct. It probably tends to dis- 

 appear in connection with the degeneration of the branchial appar- 

 atus. 



Stage XII. — Tailed toad, 7 mm. Close of metamorphosis. 



The quadrate cartilage now stands almost vertical, its distal, 

 articular extremity lying under the posterior border of the eye. 

 The hyoid bar has separated completely from the quadrate and its 

 dorsal extremity is now joined by the intervention of a dense 

 strand of cells to the base of the auditory capsule. 



The distal part of the tympano-Eustachian tube now lies imme- 

 diately posterior and ventral to the eye. Since the distal portion 

 of the quadrate rotates backward more rapidly than the remaining 

 part, it results that the posterior, hitherto ventral, surface of the 

 cartilage forms a shallow concavity. From this behavior it follows 

 that the distal, expanded portion of the tube — i.e., tympanic por- 

 tion— comes to lie farther posterior in relation to the rest of the 

 cord, so that the latter no longer presents an almost direct antero- 

 posterior course, but instead now hes in an almost transverse plane, 

 except for a slight antei'ior inclination. The tympanic region of 

 the tube is thus brought into relation with the auditory capsule. 

 In the present period it has not quite reached the region of the 

 latter, but is not far removed, being located just back of the eye. 

 Another feature shown by the present stage is the union of the 

 various fragments of which it was hitherto composed. This union 

 is also probably to be connected with the quadrate's change of 

 axis, since this would result in carrying the more anterior frag- 

 ments backward and thus bringing thera into closer relation with 

 the posterior parts. At present the tube can be traced without a 

 break throughout its entire course. This fact speaks strongly for 

 the view that these parts have all along been united by an attenu- 

 ated cord. The fragments are simply the contents of this cord 

 which hav^e been restricted to certain areas. As a result of the 

 backward rotation of the quadrate, the stretching to which the cord 

 had hitherto been subjected is relieved and accordingly the vari- 

 ous fragments of the substance flow together, thus producing the 

 union described. Proxiraally, however, ' the tube forms no con- 



