86 PRACTICAL CARP CULTURE. 



semicircular canals do not appear unless a slight fold of the enclosing 

 membrane can be said to represent them in a rudimentary condition. 

 Moreover the whole organ has no bony envelope as in most fishes, but is 

 merely enclosed in a cartilaginous or gristly capsule connected with the 

 brain-cavity. Sound-causing vibrations can therefore reach the centre 

 by two channels either through the solid bone of the skull or more directly 

 through the softer capsule of the ear. 



It is, however , perfectly relevant to the purpose of this chapter to 

 dwell at rather more length on the ear of the carp which presents some 

 peculiarities deserving notice. In this fish and others more or less nearly 

 allied to it, there is a very singular apparatus seemingly adapted to assist 

 the hearing. The air-bladder of the carp consists of two parts only 

 slighly connected. The fore part is a short cylinder with rounded ends 

 and supported by a projecting process from the third vertebra. Attached 

 to the front of this part of the bladder are two small bones that point for- 

 ward and upward toward the back of the skull. These communicate with 

 two small chambers in the occipital or hindmost bone of the head which 

 are in direct connection with the cavity of the ear. By means of these 

 bones a line of communication is maintained between the air-bladder and 

 the ear. This apparatus can be traced out by careful dissection. Moreover 

 in the carp the back of the skull is completely open or at least contains 

 two large passages that occupy a great part of its area, whereas in most 

 other fishes it is shut in by a bony wall. These details are shown in fig- 

 ure A or figure D. 



The carp therefore has two means of receiving waves of sound one 

 through the bones of the skull and the other through the air-bladdder. 

 ft is not possible at present to say if these two supplement one another 

 each doing a different kind of work or reinforce one another each con- 

 veying similar vibrations so as to produce a stronger impression on the 

 conscious centre. 



In the carp it is moreover worthy of notice that the extent of the 

 semicircular canals is very great. The bony tubes in which they lie are 

 not excavated in the immediate wall of the skull as is usually the case, 

 but the cranial bone is extended into broad wings two of which are verti- 

 cal and the third horizontal. The three together form a sinus or chamber 

 outside of the cavity of the skull which is open below but closed above, 

 behind and outside. This structure gives a great apparent width to the 

 head when viewed from behind without at all increasing the actual brain 

 capacity. But at the same time it gives an opportunity for much expan- 

 sion of the semicircular canals so that these bony wings with their enor- 

 mous enclosed sinus may be regarded as a special development of the ear. 

 It must not hence be inferred that this anatomical structure is peculiar to 

 the carp. It may be found in other nearly related fishes but it is in strong 

 contrast with the contracted limits of the bony canals in the herring, the 

 pickerel, &c. 



The sac of the otolith in the carp is also much depressed and is situ- 



