REAUMUR 255 



discovered them feeding on the leaves. It is little 

 observations of this kind which keep alive the attention 

 of the reader. In the same memoir we have a lively 

 description of the arts practised by different caterpillars 

 when alarmed. Some curl themselves up, others sham 

 dead ; others let themselves fall to the ground ; others 

 run away. A few stand on the defensive, and execute 

 movements of various kinds, which possibly inspire 

 terror. 



Reaumur had to contend with one very serious 

 difficulty. Many of the insects which he wished to 

 point out had no fixed names, either popular or scientific. 

 Sometimes he hits upon a name of his own, and these 

 are often happily chosen, but now and then it is im- 

 possible for the reader to make out with certainty what 

 insect Reaumur had in his mind. The concise characters 

 of genera and species, which he found so dry, have their 

 value after all. 



From the external structure of a caterpillar Reaumur 

 proceeds to consider its internal organs. He had 

 Malpighi's admirable description of the silkworm as a 

 guide, but the dissections figured in the Bihlia Natures 

 were as yet inaccessible. No better elementary account 

 of the legs, head and spiracles of the caterpillar than 

 Reaumur's could be set before a young student of the 

 present day. Now and then, of course, some faulty or 

 deficient explanation reminds us that he wrote nearly 

 two centuries ago. He knows, for example, nothing 

 about the chemical properties or mode of formation of 

 the substance (chitin), which forms so large a part of the 

 external skeleton of an insect. 



The silk-glands, the spinneret, and the silk itself are 

 thoroughly investigated. A simple expedient is pointed 

 out which greatly facilitates the dissection of the glands. 



