io8 THE ASCENT OF MAN 



ancient habitat, it actually manufactures it. That 

 the creature itself has discovered the anomaly of 

 its shell is obvious, for in almost every class its 

 state of dilapidation betrays that its up-keep is no 

 longer an object of much importance. In nearly 

 every species the stony houses have already lost 

 their doors, and most have their shells so reduced 

 in size that not half of the body can get in. The 

 degeneration in their cousins, the slugs, is even more 

 pathetic. All that remains of the ancestral home 

 in the highest ranks is a limpet-like cap on the tip 

 of the tail ; the lowest are sans everything ; and in 

 the intermediate forms the former glory is ironic- 

 ally suggested by a few grains of sand or a tiny 

 shield so buried beneath the skin that only the 

 naturalist's eye can see it. 



When Man left the water, however — or what 

 was to develop into Man — he took very much 

 more ashore with him than a shell. Instead of 

 crawling ashore at the worm stage, he remained in 

 the water until he evolved into something like a 

 fish ; so that when, after an amphibian interlude, 

 he finally left it, many " ancient and fish-like " 

 characters remained in his body to tell the tale. 

 The chief characteristic of a fish is its apparatus 

 for breathing the air dissolved in the water. This 

 consists of gills — delicate curtains hung on strong 



