350 H. D. REED 



to those of Spelerpes, except that the fenestral plate is formed 

 in a less degree from the invading isthmus and more from car- 

 tilage appearing independently within the fenestral membrane 

 itself. Other genera of the family Plethodontidae have been 

 studied and found to agree in all fundamentals with Spelerpes. 

 As comparisons with Desmognathus and Spelerpes the observa- 

 tions of Peter ('98) are both interesting and significant. His 

 studies were made upon Ichthyophis glutinosus, one of the Gym- 

 nophiona. He concluded that the sound-transmitting apparatus 

 in this species represents two distinct components, one otic, the 

 other extraotic in origin. The latter is first laid down as a con- 

 tinuous and dense cord of cells extending from the quadrate 

 cartilage to the fenestral region. Chondrification begins at the 

 fenestral end and proceeds toward the quadrate. The fenestral 

 element in the stages figured by Peter is joined, to the stylus, 

 although in earlier stages the two are distinct according to de- 

 scriptions. In the adult state, as shown by the descriptions and 

 figures of the Sarasins ('87 to '93), the plate completely fills the 

 fenestra. Peter concludes that the element in the fenestral mem- 

 brane is to be likened to the operculum, and that the lateral pro- 

 jection or stylus represents the columella of urodele types. With 

 regard to the presence of two elements in Ichthyophis and their 

 independent origin, there is complete agreement with the Caudata. 



FAMILY AMPHIUMIDAE 



The fully formed fenestral element in Amphiuma is of the 

 single-plate type with a large stylus. A typical isthmus fenes- 

 tralis is present. Kingsbury and Reed described this structure 

 in the adult, and according to material available at that time, 

 were unable to make any statement regarding homology other 

 than that the plate appeared to represent the columella. More 

 recently additional material has been examined revealing new 

 facts which should be presented. For the nature of the plate in 

 the definitive state, see figure 29. 



Embryos of a given stage in development of this species are 

 relatively much longer than those of other urodeles, and the 

 length of an embryo or larva does not serve as an index of devel- 

 opment when compared with other urodeles. 



