2 AYERS. [Vol. VI. 



tied Das GeJiororgan der Wirbelthiere. Feeling the need of a 

 "geniigende Grundlage" for the comparative study of the ver- 

 tebrate ear, in my endeavors to understand the problems of 

 vertebrate cephalogenesis, I have sought for, and have, I believe, 

 at last found, the basis from which the characteristic structures 

 of the internal ear take their origin, and the law according to 

 which this development takes place throughout the vertebrate 

 group. The study of the morphology of the internal ear of 

 vertebrates has naturally made much more progress than the 

 study of its phylogeny. In fact, until the publication of Beard's 

 paper on the branchial sense organs, we had no sure basis for 

 homologizing the ear with other sense organs of the vertebrate 

 body. Hence, the internal ear has always been looked upon as 

 a Ding an sich even by those investigators who were constantly 

 endeavoring to gain a clearer insight into its phylogenesis. 



In 1883 J. Beard arrived at the conclusion that the verte- 

 brate auditory organ was only a modified portion of the system 

 of superficial sense organs, for which he proposed the name 

 branchial sense organs. Beard arranged the sense organs of 

 the vertebrate head according to their mode of development 

 and their relations to the cranial nerves. He found that the 

 nose and the ear sense organs were related to the surface of 

 the body and the central nervous system through the media- 

 tion of the cranial nerves, in much the same way as the sense 

 organs of the superficial system, which he called the branchial 

 sense organs. He did not go further than to state that these 

 two pairs of higher sense organs were derived from branchial 

 sense organs. We shall see further on how far Beard was 

 from a conception of the true nature of the auditory organs. 

 On this occasion, I shall confine myself to a consideration of 

 the auditory organ alone, leaving the nasal organ for a separate 

 paper. 



In the paper cited above. Beard says, p. 143 : " The audi- 

 tory organ is, like the segmental sense organs, really a modified 

 portion of the epiblast. Very early in development it becomes 

 shut off in a sac from the epidermis, a condition which only 

 arises later in the segmental sense organs." Beard clearly 

 enough failed to appreciate the significance of the early in- 

 folding of the auditory sense organ into its auditory vesicle. 



