202 MH. F. DAT ON AMPHIBIOUS AND 



ice in the Polar regions. Both adopt the same plan ; both have 

 blow-holes ; and it is at these places that man watches for and 

 captures his prey. 



The generality of fish, as is well known, undoubtedly respire air 

 which is in solution in the water in which they reside, and find such 

 sufficient for respiratory purposes, except under some peculiar 

 circumstances, when they obtain it direct from the atmosphere. 



On June 27th, last year, I accompanied Dr. Dobson to the 

 Dublin Zoological Gardens, In one of the tanks at the aquarium 

 were three common eels (Anguilla vulgaris), whose usual mode of 

 respiration appeared to be as follows : — Opening their mouths, 

 they took in the amount of water they required, transmitting it 

 backwards through the gill-opening. In this course it passed 

 the branchiae, and thus the blood was oxygenated. One, how- 

 ever, appeared indisposed ; for instead of taking in water like his 

 companions, he raised his head to the surface, and each time he 

 did so he opened his mouth and a current of bubbles was sent 

 backwards through his gill-openings. Here were three specimens 

 of the same species placed in identical situations, whilst they 

 showed difierent modes of oxygenating their blood ; the air con- 

 tained in the water sufficed for two, whereas the third was obtain- 

 ing it direct from the atmosphere. 



In 1871, at Calcutta, I procured some living specimens of eels 

 {OphichtJiys horo). The gills of this fish are contained in large 

 cavities, one on either side of the head, those on one side being 

 divided from those on the other by an impervious septum. On 

 watching its movements, it was seen to distend this receptacle* 

 with air taken in at the mouth, or, if in water, to live equally 

 well by passing this fluid through the gill-cavity. On holding 

 its small gill-opening firmly closed, it took in air by its mouth in 

 distinct gasps : if its mouth were closed, it struggled until it was 

 released, as, of course, without its use it could not respire. On 

 exposing the gills by cutting away the gill-membranes, and then 

 placing it in water, it could be seen to slowly move its branchiae, 

 even when in such a situation that it could not obtain atmospheric 

 air direct. It appeared to be able to employ for respiration air 

 dissolved in water or air inspired directly from the atmosphere. 



We see, when the water gets foul or warm in the summer, or 



insufficient in quantity for the contained fish, they take in air 



* In fishes having small external branchial openings the cavity containing 



the gills is usually large ; and these fish, as a general rule, live some time after 



their removal from vrater. 



