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



iiim. Operculum and opercular muscle present. D, group VII; 

 columella present, joined to otic capsule, connected with the sus- 

 pensorium; the opercular muscle present, the operculum not devel- 

 oped as such. Up through the groups I to V, evidence of indubitable 

 value is presented of the incorporation and loss of an element (colu- 

 mella) with an attendant loss of its primary connection, a substi- 

 tute making its appearance (the operculum). The m. opercularis, 

 absent in groups I, II and VI, present in the others, appears to 

 deserve the name given it by Gaupp ('93), since in the Urodela it 

 possesses characteristic attachments and is not a portion of another 

 muscle (Levator anguli scapulae). When an operculum is developed, 

 an opercular muscle is present, while its insertion in group VII is 

 suggestive, as is also equally, its absence in groups I and IT. From 

 the examination of larvse, it should be stated, however, that it appears 

 to be absent in all urodeles in the larval state. It will be referred 

 to subsequently in connection with the problem of the function of 

 the urodelan "sound-transmitting" apparatus. 



Comparison with Anura. In the first contribution a comparison 

 was made of the conditions found in Ambystoma to the "columella 

 auris" of the frog, and further investigation has strengthened us in 

 the acceptance of the homologies then advanced,— the columella with 

 the plectrum (pars interna plectri), the operculum being homolo- 

 gized in the two groups. The resemblances and differences between 

 the two forms may perhaps best be presented in tabular form, in 

 parallel columns the resemblance being presented first, enumeration of 

 differences following. The relations in the frog are taken from 

 Gaupp ('93, '05). 



The first of the differences {'Eo. 1) is of no marked significance, 

 since in other Anura (e. g., Dactylethra, Parker, Gaupp '98) the 

 plectrum may overlap the operculum. The next two contrasts par- 

 take more of the nature of resemblances than of differences, hence 

 items 10 and 11 are the only points of difference needing comment 

 here, a detailed discussion not being intended, since they are doubt- 

 less the ones that will be regarded as the most weighty. 



As to the tenth item, it is only necessary to recall the numerous 

 instances of precocious and postponed development of homologous 



