476 MANUAL OF ZOOLOGY. 



The essential portion of the organ of hearing (labyrinth} is 

 present in almost all fishes, but in none is there any direct 

 communication between the ear and the external medium. 

 In some cases, however, there is a communication between 

 the ear and the swim-bladder, thus foreshadowing the Eusta- 

 chian tube in man. 



As regards their reproductive system, fishes are, for the most 

 part, truly oviparous, the ovaries being familiarly known as the 

 " roe," The testes of the male are commonly called the " soft 

 roe," or " milt." The products of the reproductive organs are 

 often set free into the peritoneal cavity, ultimately finding their 

 way to the external medium by means of an abdominal pore (or 

 pores) ; or they are directly conveyed to the exterior by the 

 proper ducts of the reproductive organs. 



