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they can lengthen or widen as they find occasion. They 

 lengthen it by adding to each end new layers of silk and 

 hair, and widen it as we do a glove, by cutting it in the 

 middle accordin" to the length of it, and by engrafting 

 a piece. You may imagine that I am speaking of 'house* 

 moths : field-moths, which clothe themselves with leaves, 

 surpass them in industry. 



Several kinds of Jiskps and lirds change, at a stated 

 time, their dwelling-places. We have seen numerous 

 shoals of herrings and cod-fish, aodjjodta of geese, quails, 

 and crows, re&embling thick clouds that sometimes 

 darken the air. By such periodical emigrations the 

 species are preserved, and in their long pilgrimages 

 nature is their pilot and provider. 



3. The grasshopper, lizard, tortoise, and crocodile, 

 furnish examples of animals that scarce take any care of 

 their eggs, and are almost wholly unmindful of the 

 young that are hatched from them. They lay them iri 

 the earth or sand, and leave the sun to communicate 

 the warmth necessary for them. Shell-fish practise the 

 same method : some spawn in the water; others between 

 Stones, or in the sand. 



The instinct of the different species consists in de- 

 positing them in places where the young may find pro- 

 per nourishment al their birth. The mothers commit 

 no mistake with respect to that. The butterfly of the 

 call age- cater pillar never lays her eggs on meat, nor the 

 Jlesh-Jly on the cabbage. 



The gnat, that flutters in the air, was at first an in- 

 habitant of the water. For this reason her eggs are 

 always deposited in the water. The mass formed by 

 them resembles a little vessel which the insect sets 

 afloat. Each egg is in the form of a keel. All the 

 keels are vertical, and are disposed back to back. The 

 gnat lays but one egg at a time. We cannot devise how 

 k vhe cak cause the first egg or keel to remain in the water 



