526 PROF. T. W. BBIDaE ON THE 



in the pterotic bone and has no special relations with the auditory 

 organ. The other vesicle occupies a globose chamber in the 

 prootic, and there becomes closely applied to the wall of the 

 corresponding utricular diverticulum, which enters the chamber 

 through an auditory foutanelle in the prootic. In some 

 instances there appears also to exist a connection between the two 

 utriculi in the form of a transverse sub-cerebral canal, which, 

 however, is not to be regarded as homologous with the similarly 

 situated ductus endolymphaticus of the Cyprinoid and Siluroid 

 Teleosts. Such a utricular connection was first discovered in 

 Clupea harengus by Weber (12. p. 77), and subsequently 

 by Ereschet (1) in C. alosa. On the other hand, the evidence 

 as to the existence of a supra-cerebral connection between 

 the two sacculi, as affirmed by Hasse (6), or between the two 

 utriculi, as stated by Breschet (1. p. 17), is too conflicting to 

 admit of any definite conclusion being drawn *. 



The preceding arrangement, which appears to be restricted to 

 the physostome family of the Clupeidae, was first described by 

 "Weber in the Herring {Clupea harengus). Recently, Eidewood 

 (9. p. 26) has contributed an excellent revision of the anatomical 

 relationships of the two organs in the six British species of 

 Clupeidae, viz. : — Clupea harengus, Linn., the Pilchard (C. pil- 

 chardus, Walb.), the Sprat (C. sprattus, L.), the Allis Shad 

 (C. alosa, L.), the Thwaite (C. finta, Cuv.), and the Anchovy 

 {Engraulis enchrasicholus, Cuv.). Tliese species apparently 

 include all the Clupeidae in which a connection between the 

 auditory organ and the air-bladder has so far been described. 



C. In a third and last series of Teleostean fishes, viz., the 

 physostome families of the Cyprinidse, Characinidse, Siluridse, and 

 Gymnotidse, the connection between the air-bladder and the 

 auditory organ attains its maximum complexity and physio- 

 logical importance, and is effected, not by auditory caeca, but by 

 means of a chain of movable Weberian ossicles. The auditory 

 organs of opposite sides of the head are connected together by the 

 mesial union of the two endolymphatic ducts, one from each 

 sacculus, and the consequent formation of a transverse sub- 

 cerebral connection between the two sacculi. Prom the point of 

 union of the two ducts a median sinus endolymphaticus, enclosed 

 in a similar median extension of the perilymphatic spaces of the 



* For a discussion of this point, vide Eidewood (9. pp. 38-39). 



