1901.] NATURAL SCIENCES OF PHILADELPHIA. 257 



posterior direction taken by the tubal Anhuje is cliaracteristic of it 

 during the entire larval period, 



8. The further degeneration of the hyomaudibular fold is corre- 

 lated with the subsequent increase in size of the muscles already 

 mentioned, the union of the hyoid cartilage with the quadrate and 

 the enlargement of the mandibular aortic arch. 



9. After the degeneration of the hyomaudibular fold the 

 Anlage of the tympauo- Eustachian passage persists as a minute, 

 solid cord, extending along the outer surface of the pi-ocessus 

 muscularis of the quadrate. Posteriorly it is attached to the wall 

 of the pharynx at a point posterior to the quadrato-hyoid articu- 

 lation. Anteriorly and distally it expands to form the club-shaped 

 Anlage of the tympanic cavity. 



10. During the active tadpole period the tympano-Eustachian 

 Anlage undergoes marked degeneration. This degeneration is 

 confined to the middle and posterior parts of the Anlage, the 

 distal expanded portion retaining its original relative size through- 

 out the entire larval period. The degeneration is in all probability 

 connected with the growth of the two muscles — depressor man- 

 dibul?e and ossis hyoidei — between which it lies. Owing to the 

 lack of space it is unable to keep pace with the surrounding struc- 

 tures in the subsequent growth of the animal. 



11. In the early tadpole period the tympano-Eustachian Anlage 

 is continuous posterioily with the wall of the pharynx. Later the 

 connection between the two apparently disappears, though the time 

 of its disappearance seems to vary in different individuals. An 

 indistinct strand may continue to unite the two parts, but this 

 I have been unable to demonstrate. 



12. The degeneration of the tympano-Eustachian Anlage is 

 carried to an extreme in the later tadpole stages. Xi this time it 

 is apparently broken up into a number of fragments of varying 

 length. This fragmentation is probably more appareuC than real, 

 being produced by the restriction of the more vital staiuable sub- 

 stance of the tubal Anlage to areas less subject to the pressure of 

 the neighboring structures. The irregular distribution of tha 

 fragments, both in different individuals and on different sides of 

 the same individual, favors the view that a compressed, transparent 

 cord still connects the apparently separate parts. In one specimen 



17 



