( 27 ) 



of water in moisture for lengthened periods, and for only a 

 short and variable time in water, provided they are unable 

 to obtain air direct : that the cavity above the gills does not 

 contain water, but has a moist secreting surface in which the 

 air is retained for the purposes of respiration, whilst it seems 

 probable that the air, after having been employed for this 

 purpose, is ejected through the mouth. Some of the venous 

 blood appears in these fishes to be oxygenated at the gills, 

 and the remainder in the superbranchial cavity by means of 

 air ; but if they are kept under the water without being able 

 to obtain direct access to it, this cavity, which is surrounded 

 by bony tissue, becomes filled with water, which cannot 

 be discharged owing to its almost non-contractile powers. 

 Thus, there being no means .of emptying it, and the contained 

 water probably becoming carbonised, the whole of the respi- 

 ration is thrown upon the gills. This accounts for the fact 

 that when the fish is in a quiescent state it lives longer than 

 when excited, whilst the sluggishness sometimes evinced, may 

 be due to poisoned or carbonised blood. An analogous 

 instance may be seen in an eel, Ophichthys boro, in which 

 the gills are contained in a large cavity in either side 

 of the head, and which do not communicate with one ano- 

 ther. The fish distends this receptacle with air taken in 

 by the mouth. It appears to be able to respire either directly 

 from the atmosphere, or by means of the air contained 

 in the water. On its small gill-openings being kept closed, 

 it takes in air by the mouth ; should its mouth be held 

 shut, it struggles until its head is released so as to 

 be able to respire. If the gills are exposed by cutting 

 away the outer gill-coverings, and it is then returned to 

 the water, it begins to slowly move its branchiae, and appears 

 to feel little, if any, inconvenience in being unable to obtain 

 air direct through its mouth. In some of the siluroids, there 

 exists an accessory breathing apparatus ; thus, the Clarias 

 possesses a dendritic one on the convex side of the second 

 and fourth branchiae, which has much the appearance of a 

 bunch of red stick-coral ; this is received into a cavity 

 posterior to that existing solely for the gills. In the 

 Saceobravchus or scorpion-fish, a long air-vessel of a pul- 

 monic character (in addition to the air-vessel proper which 

 is enclosed in bone) extends throughout the length of the 

 muscles of the back, and anteriorly opens into the gill-cavity. 

 In the eel-like Symbranchidce, the Amphipnous cuchia has 

 a pulmonic sac for the reception of air connected with the 



