37 The Naturalist of Cumbrae. 



Dr. Claus, in his " Elementary Text-book of Zoology," trans- 

 lated by Sedgwick and Heathcote, in describing the sense-organs 

 of vertebrates, says 



" The auditory organ, the nerve of which belongs to the hind- 

 brain (probably derived from the sensory root of a spinal-like 

 cranial nerve), is entirely absent in Amphioxus. In its simplest 

 form it is a membranous sac (membranous labyrinth) containing 

 fluid and otoliths. The posterior part of this sac is usually 

 prolonged into three semicircular canals, while the anterior 

 part, which in many cases is separated as the saccule, gives off 

 a prolongation which forms the cochlea (fig. 578, s. c.)." In the 

 accompanying " diagram of the auditory labyrinth (after Wal- 

 deyer)," that of the fish has a quite distinct cochlea, though a 

 small one. When discussing the sense-organs of fishes, as 

 distinct from other vertebrates, Claus says, " The auditory 

 organ (absent only in Amphioxus} consists only of the labyrinth 

 (fig. 578, i.), and in Teleosteans, Ganoids, and Chimaera lies 

 partly in the cranial cavity, surrounded by fatty tissue. It is 

 worthy of notice that in Cyprinoidce, Characin<z y Siluridce, 

 and others, the labyrinth is connected with the swimming- 

 bladder by a chain of small bones " (pp. 121, 139). 



