606 B. F. Kingsbury and H. D. Keed. 



by Stohr and more recently by Fuchs ('07) as contrasted witli an 

 appearance secondarily, by dehiscence or absorption, is abundantly 

 established. It must be understood, however, that this applies only 

 to the primary fenestra, while in the formation of the secondary and 

 definitive fenestrse, in some forms, at least, the extension is accom- 

 plished essentially as a "dehiscence." The developmental trans- 

 formations undergone by the primary fenestra require a more 

 detailed study in a number of salamanders before a full interpreta- 

 tion can be made. 



In the Plethodontidse and Desmognathidae, where the single fenes- 

 tral plate possesses some of the characters of operculum and colu- 

 mella combined, the development has been followed in Spelerpes 

 bislineatus. There is no evidence of a fusion of two structures, the 

 cartilaginous and bony plate which bears the stilus by growth gains 

 the territory which in Ambystoma is occupied by the operculum and 

 may therefore be regarded as representing that structure without 

 embodying it." 



On plate X are set forth in schematic form the morphological rela- 

 tions of the two structures under consideration as they occur in 

 typical forms. Examining the conditions in the Urodela, we find 

 that they may, with the figures of this plate as illustrations, be 

 divided into seven groups, the characters being compared in tabular 

 form on page 607. 



Under these seven groups the forms studied distribute themselves 

 as follows: Group I; l^ecturus, Proteus ( Typhi omolge). Group 

 II ; Larval Ambystoma and urodele larvae in general, Cryptobranchus, 

 Megalobatrachus, Amphiuma. Group III; Adult Ambystoma, Adult 

 Chondrotus, probably other members of the Ambystomidse. Group 

 IV; Salamandra, and possibly some of the Ambystomidae. Group 

 V ; Dieraictylus, Triton, undoubtedly Salamandrina and other Pleur- 

 odelidse. Group VI; Siren. Group VII; the Plethodontidse (as 

 examined), — Typhlotriton, Spelerpes, Gyrinophilus, Hemidactylium, 



"The differences between the Ambystomidse and the Plethodontidae in respect 

 to the presence and absence of an operculum, are paralleled in the Anura by 

 the similar differences in the Frog (as an example of the type) and Pipa. 

 Gaupp's very interesting discussion of the interpretation in the last case 

 ('98, p. 1065) presents the problem for the first case as well. 



