1230 The Zoologist— Junk, 1868. 



in these delicate organs. Not only is the outer skin cast off, but also 

 the lining of the air-tubes and intestines, together with all the chewing 

 organs and other appendages of the head. After the moulting the size 

 of the larva is considerably iucreased ; the head is large, compared 

 with the body, but eight or ten days later it will look small, as the 

 body will have increased very much in size. This is a certain indi- 

 cation that the worm is about to moult. Every ten days the same 

 operation is repeated ; from the fourth moulting to the time of 

 beginning the cocoon the period is about sixteen days. The worms 

 seem entirely unable to discern objects with their simple eyes, but 

 they can distinguish light from darkness, as a very simple experiment 

 will show. If a worm be put in a box with two holes in it, one of them 

 turned to the light, the other to the dark, the caterpillar will very soon 

 come out through the hole turned to the light. 



It is astonishing how rapidly the larva grows, and one who has no 

 experience in the matter could hardly believe what an amount of 

 food is devoured by these little creatures. One experiment which 

 I made can give some idea of it: when the young silk-worm hatches 

 out it weighs one-twentieth of a grain; when 



10 days oKI il weighs $ a grain, or 10 times die original weight. 

 20 „ 3 grains, „ 60 „ 



30 „ 31 „ „ 620 



40 „ 90 „ „ 1800 



56 „ 207 „ „ 4140 



When a worm is thirty days old it will have consumed about ninety 

 grains of food; but when fifty-six days old it is fully grown and has 

 consumed not less than one hundred and twenty oak-leaves, weighing 

 three-fourths of a pound; besides this it has drank not less than one- 

 half an ounce of water. So the food taken by a single silk-worm in 

 fifty-six days equals in weight eighty-six thousand limes the primitive 

 weight of the worm. Of this about one-fourth of a pound becomes 

 excrcmcntitious matter; two hundred and seven grains are assimilated 

 and over five ounces have evaporaied. What a destruction of leaves 

 this single species of insect could make if only a one-hundredth part 

 of the eggs laid came to maturity ! A few years would be sufficient 

 for the propagation of a Dumber large enough to devour all the leaves 

 of our forests. When fully grown the worm, which has been devouring 

 the leaves so voraciously, becomes restless and crawls about the 

 branches in search of a suitable place to build up its cocoon; before 

 this it is motionless for some time, holding on to the twig with its 



