Evolution Going On 201 



force and takes fresh gulps. At the same time, like an ordinary 

 fish, it has gills which allow the usual interchange of gases 

 between the blood and the water. Now this Australian mudfish 

 or double-breather (Dipnoan), which may be a long way over a 

 yard in length, is a direct and little-changed descendant of an 

 ancient extinct fish, Ceratodus, which lived in Mesozoic times, as 

 far back as the Jurassic, which probably means over five millions 

 of years ago. The Queensland mudfish is an antiquity, 

 and there has not been much change in its lineage for millions 

 of years. We might take it as an illustration of the inertia 

 of evolution. And yet, though its structure has changed but 

 little, the fish probably illustrates evolution in process, for it 

 is a fish that is learning to breathe dry air. It cannot leave the 

 water; but it can live comfortably in pools which are foul with 

 decomposing animal and vegetable matter. In partially dried-up 

 and foul waterholes, full of dead fishes of various kinds, Neocera- 

 todus has been found vigorous and lively. Unless we take the 

 view, which is possible, that the swim-bladder of fishes was origin- 

 ally a lung, the mudfishes are learning to breathe dry air. They 

 illustrate evolution agoing. 



The herring-gull is by nature a fish-eater ; but of recent years, 

 in some parts of Britain, it has been becoming in the summer 

 months more and more of a vegetarian, scooping out the turnips, 

 devouring potatoes, settling on the sheaves in the harvest field 

 and gorging itself with grain. Similar experiments, usually less 

 striking, are known in many birds; but the most signal illustra- 

 tion is that of the kea or Nestor parrot of New Zealand, which 

 has taken to lighting on the loins of the sheep, tearing away the 

 fleece, cutting at the skin, and gouging out fat. Now the parrot 

 belongs to a vegetarian or frugivorous stock, and this change of 

 diet in the relatively short time since sheep-ranches were 

 established in New Zealand is very striking. Here, since we know 

 the dates, we may speak of evolution going on under our eyes. 

 It must be remembered that variations in habit may give an 



