ATE-BLADDEE Ilf NOTOPTERUS BORNBENSIS. 531 



similar to those of Mormyrus, are also said to be present in 

 Gymnarchus niloticus (Stannius, I. c. *). 



Mention may also be made o£ the prevalence of median 

 fontanelles in the cranial root in many Siluroids, although in 

 these Fisbes the structures in question have no special relation 

 to the auditory capsules f. 



It is certainly worthy of remark tKat the existence of cranial 

 fontanelles, as a possible avenue for the transmission of sound 

 vibrations from the water to the auditory apparatus, has been 

 recorded not only for those Fishes in which the air-bladder has 

 no connection with the membranous labyrinth (e. g., Mormyrus, 

 Macrurus), but also, and apparently quite as frequently, even in 

 those Teleosts in which such a connection is known to exist 

 (e. g., Clupea, Myodon, and Notopterus), 



IX. Eemaeks on the supposed Auditory Functioj^ 

 OF THE Air-bladder. 



The physiological value of the connection between the air- 

 bladder and the auditory organ is still one of the unsolved 

 problems of comparative physiology, and this statement seems 

 to be equally applicable to any of the three principal methods 

 by which such a connection is established. The reason for this 

 is, no doubt, that practically nearly all attempts to solve the 

 problem have been based upon anatomical evidence alone ; 

 and, as must be admitted, morphological data are often unre- 

 liable, and even misleading, when employed as the sole basis for 

 physiological deductions, and not infrequently appear to support 

 with remarkable impartiality conclusions of a widely different 

 character. When the problem has received the attention of the 

 experimental physiologist, then, and then only, may a final and 

 satisfactory solution be expected. 



The question has been most frequently discussed in connection 

 with the Ostariophysege J, and, so far, comparatively little atten- 

 tion has been devoted to those Teleosts (e. g., Sparus, Notopterus, 

 Hyodon, Glupea, &c.) in which the connection of the air-bladder 

 and auditory organ is efi'ected by other means than the presence 

 of Weberian ossicles. In venturing to discuss certain physio- 



* According to Erdl, see Stannius, I. c, footnote to p. 170. 



t Professor Howes has reminded me of the large lateral occipital fontanelles 

 in the Oyprinidje {c.f. Sagemehl, Morph. Jhb. Bd. xvii. p. 495). 



\ The physostomous families of the Cyprinidse, Silurida, Characinidse, 

 and Gymnotidffi, in which a Weberian mechanism is present. 



