THE LUNGFISH 7/ 



envelops the body closely, extending into all exposed 

 crevices. The only opening is a short funnel where the 

 cocoon extends between the Ups and teeth, and through 

 which the fish breathes. 



The lungfish is in no sense a land-living animal, and 

 if exposed naked to the air it will die in twenty-four 

 hours, its skin shriveled like that of a dry frog. But 

 within its cocoon of slime, and excluding minute evap- 

 oration through the cocoon, the only route of water loss 

 in the estivating animal is by way of the lungs, and so 

 long as the cocoon remains intact the fish is eflFectively 

 protected against desiccation. From the time when it 

 nosedives into the mud there is no possibihty, of course, 

 of obtaining food, and henceforth it must live on its own 

 tissues. Being a cold-blooded animal, it does not need 

 to maintain a high level of metabolism in order to sustain 

 the body temperature; and consequently, beginning 

 with the first day of fasting, whether active or not, its 

 metabohc rate begins to decrease, dropping by 50 per 

 cent in a week or so, and decreasing slowly thereafter 

 until within three months it reaches the low level of 10 

 to 15 per cent of that in the fed, active state. This re- 

 duction of metabohsm during fasting, which is probably 

 characteristic of all cold-blooded animals, is wholly un- 

 related to estivation as such, to the retention of meta- 

 bohc waste products, or to the cessation of nervous ac- 

 tivity; it appears to result purely and simply from the 

 absence of food and the progressive depletion of the 

 body stores of fat and protein and is perfectly duphcated 

 in fasting but active fish. It is a highly important factor 

 because it serves to increase, four to six times, the period 

 the imprisoned animal can hve before it must inevitably 

 starve to death unless it is hberated. 



As the metabohc rate and therefore the oxygen re- 

 quirement decrease with fasting, breathing becomes 

 slower and slower: whereas an active fish breathes at 

 the surface of the water at least every fifteen minutes, 

 the intervals between breaths during estivation extend 



