1200 LIFE : OUTLINES OF GENERAL BIOLOGY 



young freshwater mussels, and the mussel nurses the young bitter- 

 lings; the water-wagtail, in swallowing the small water-snails that 

 harbour the larvae of the liver-fluke, is helping the sheep-farmer; 

 the squirrel has its share in making the harvest a success. Suppose 

 that the glory that was Greece was parth^ dimmed by malaria; the 

 disease is sown by mosquitoes; the larval mosquitoes in the water 

 are very effectively checked by minnows. Ye gods and little fishes ! 



Many of us are familiar with the "death-watch" beetles that 

 make tapping noises on the wainscot, the male insect thumping his 

 head against the wood as a signal to his desired mate. The larval 

 death-watches bore in wood and other dry materials, including 

 books —poor food. Now it has been shown that the beginning of the 

 digestive part of the grub's food-canal bears two minute pouches 

 which are crammed with yeast-cells. These probably effect the 

 fermentation of the dry-as-dust food, and it may be said of many 

 insects that they are peripatetic breweries. In most of these the 

 egg-shell includes yeast-cells along with the egg, and these multiply 

 as development goes on. But Prof. Buchner found that there 

 are no yeast-plants in the eggs of the death-watch, though the 

 young grubs always contain them in abundance. How is this puzzle 

 solved ? The solution is very striking. Associated with the egg-laying 

 apparatus in the female death-watch there are two minute reservoirs 

 opening to the exterior, and these are full of yeast-plants. When an 

 egg is laid, some yeast is expelled from the reservoirs and it adheres 

 to the rough outer surface of the shell. When the beetle grub, 

 developing from the egg, is ready to hatch out, it nibbles at the 

 egg-shell, and thus its food-canal is infected and eventually stocked 

 with yeast-plants. Of course, a very little leaven goes a long way 

 with a larval death-watch. If this stood alone it would be a curiosity 

 of Natural History, but such linkages are frequent and may even 

 be called characteristic of Animate Nature. 



As a fifth contribution to Culture may be ranked the array of 

 brain-stretching problems which the study of Natural History 

 provides. It cannot be maintained that Natural History offers the 

 same discipline in resolute thinking that may be found in an exact 

 science such as mathematics and physics, but it has a discipline of 

 its own, that tends to develop sound judgment. Animate Nature is 

 a rare Euclid. It bristles with unsolved problems. No one can tell us 

 why a cell divides into two, or how a ferment works, or what comes 

 about in the fertilisation of an egg, or how the obvious complexity 

 of a chick is minted and coined out of the apparent simplicity of a 

 drop of living matter lying on the top of the yolk ; and yet there 

 is a library of books on each of these subjects. 



Or to pass to less fundamental questions, the naturalist is far 

 from understanding how sea-swallows transported for a thousand 

 miles in closed baskets into previously unvisited seas are able, in 



