50 THE STUDY OF ANIMAL LIFE CHAP. 



ground life, illustrated for instance in the mole, many 

 animals have sought and found safety, and the change 

 seems even now in progress, as in the New Zealand parrot 

 Stringops, which, having lost the power of flight, has 

 taken to burrowing. Similarly the power of flight must 

 have helped insects, some ancient saurians, and birds 

 out of many a scrape, though it cannot be doubted that 

 this discovery of a new world often brought only a 

 temporary relief. 



Taking the race of earthworms, we find that three or 

 four genera, e.g. Alma and Dero, have gills, which sug- 

 gests that earthworms evolved from an aquatic ancestry. 

 And many not very distant relatives of the earthworms 

 proper are found in the mud of rivers and ponds. Sup- 

 posing, then, that earthworms discovered the possibility 

 of a subterranean life, we can believe that they had a 

 long Golden Age with a new world all to themselves. 

 But in the course of time this subterranean world was 

 invaded by centipedes and burrowing beetles, and long 

 afterwards by the moles, so that nowadays earthworms 

 are far from being free from persecution. The same is 

 true of animals that hit upon the device of lying quiet 

 during the day and coming out at night as the earth- 

 worms have had to do. For a time, doubtless, it works 

 very well, but when other creatures follow suit some 

 subtler shift must be attempted. It appears that for 

 terrestrial weaklings and slackers a cavernicolous life 

 offers asylum, but over the door of the cave there should 

 be a notice with the ominous words " Short Commons." 



There are many extraordinary examples of animals 

 taking to habitats quite strange to the ordinary habits 

 of their kind. We speak of the awkwardness of a fish 

 out of water, but many fishes are quite at home on 

 land. The climbing perch occasionally ascends a few 

 feet up a tree ; the common equatorial shore- fish Peri- 

 ophthalmus clambers on to the roots of the mangroves ; 

 eels may be found making an excursion through a 

 meadow ; and one of the North- American shore ' min- 

 nows," a species of Fundulus, is quite expert in jumping 

 seawards for several yards across the sand, if it has 



