exemplified in the Genus Elachista. 85 



change takes place in its appearance when full fed ; 7". Where it 

 changes to pupa ; 8°. What amount of cocoon it makes ; 9". What 

 is the form of the pupa ; and 10". How long it remains in the 

 pupa state. 



But besides " I'histoire de Icurs transformations," we require 

 that of " leurs moeurs, leurs habitudes." 1°. Is the larva grega- 

 rious or solitary ? 2°. Is it active or sluggish ? 3°. Does it feed 

 by night or by day ? 4^ Does it construct any cell or gallery in 

 which it feeds? 5". Is the pupa lively or not? 6°. Does the 

 perfect insect fly willingly ? 7°. What are its motions in flying 

 and walking? Neither does this by any means exhaust the sub- 

 ject ; for " il faut faire I'histoire des substances vegetales ou ani- 

 males dent ils aiment a se nourrir." 1". What is the food-plant of 

 the larva? 2". On what other plant is it sometimes found? 3". 

 What other plants will it eat when in captivity and its natural food 

 cannot be supplied? 



Now, to answer all these questions with reference to any one 

 species is no easy matter, but to answer them with respect to a 

 whole group requires a vast amount of methodized, systematic 

 observation ; for we must notice not only what we do see, but 

 what we do not see. To ascertain that a species is not double- 

 brooded, we must seek for the second brood, and notice that we 

 do not find it. All this requires time, patience and perseverance. 



Now, to apply the foregoing remarks to the genus Elachista, 

 belonging to the Tineina division of Lepidopiera. Of this genus 

 the larvae were entirely unknown to us till the spring of 1853, 

 when it was discovered that they mined the leaves of grasses, — a 

 very natural habitat certainly now that we know it, but one which 

 our inductive powers failed to point out to us till accident led to 

 its discovery. Then various grasses were searched with great 

 diligence, and with the exception of the flat-stemmed grass {Dac- 

 tylis glomeratd), which was soon found to produce more than one 

 species of Elachista, it was assumed that each different grass was 

 the pabulum of a different species of larva ; consequently at the 

 close of the season of 1853 it was received as a settled point that 

 certain grasses were the food-plants of certain species of Ela- 

 chistce. 



In a science of observation we first observe an occurrence ; we 

 then deduce from that observation certain probable events, which 

 we expect will come to pass, and proceed to repeat our observa- 

 tions to see if it is so. Thus tlie present season became the 

 touchstone for the discoveries of last year among the Elachistce. 

 The result has been that much that had been considered settled 



