28 A Guide to the Zoological Collections 



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Although the great majority of Elasmobranch Fishes have only five pairs 

 of gill-pouches, there are a few that have six or seven pairs. Again there is 

 one small section of the Elasmobranchs, namely, the Holocephali, in which 

 the external openings of the gill-pouches are concealed by a fold of skin that 

 encloses a rudimentary gill-cover. 



Again, although the Teleosteans generally have four pairs of gills, there 

 are some, such as several of the Frog-fishes (Pediculati) that lead an inactive 

 life at the bottom of the sea, that have only two-and-a-half, or even only 

 two pairs. 



Accessory Breathing Organs of Fishes. Gills are essen- 

 tially organs for aquatic respiration, but there are some 

 fishes that, living under peculiar conditions where the 

 supply of water may periodically run short, or where it 

 may suit them to take short journeys on land, are pro- 

 vided with accessory organs that enable them to breathe 

 out of water. Several such fishes are found in the 

 jheels of India. The so-called Climbing Perch (Anabas 

 scandens) and the Singhi fish [Saccobranchus fossilis), dis- 

 sections of both of which are exhibited in Case 10, are 

 good examples of these. 



Observe in Anabas the frilled and pleated mass of 

 thin bone, covered by vascular mucous membrane, that 

 lies in a special prolongation of the gill-chamber, on 

 either side of the head. Observe in Saccobranchus the 

 lung-like extensions, into the muscles on either 'side of 

 the backbone, of the gill-chambers. 



By these curious structures, if only they are kept 

 moist, the fish is able to breathe out of water, and it is 

 a well known fact that both these fishes will live for 

 days after they have been removed from water, if only 

 they are kept damp. 



The Air-bladder or Swim-bladder of Fishes, a series 

 of dissections of which have been placed in Case 10, 

 can hardly be spoken of as an accessory breathing- 



