SOME COMMON OBJECTS 65 



Without venturing into other fields in quest of 

 common objects, I shall conclude this chapter by a 

 short reference to the microscopic possibilities of 

 the Insect World. These are, indeed, vast ; practi- 

 cally unlimited. Eggs and larvse, external members 

 and internal organs, curious adaptations of members 

 to conditions of Ufe ; these provide boundless wealth 

 of material. Each species of insect has distinct 

 pecuharities. The student will find it advisable to 

 take up a special hne in this great field, following 

 it up systematically. If he takes the Lepidoptera, 

 or scale-winged insects, as his special study, he will 

 investigate and compare their salient features. 

 More than this, he should make comparisons between, 

 say, the legs, antennae, and mouth organs of this 

 class with those of other insect classes. All along 

 the question, What is the use ? should be asked. 

 Why do certain insects have specially developed 

 organs, and how are they advantaged thereby ? 



As an example of the study of a single species in 

 all its salient features, let us consider the Common 

 House-Fly, which belongs to the diptera, or two- 

 winged insect class. We start with the eggs which 

 are found on decaying vegetable or animal matter. 

 These eggs are beautiful objects, particularly as seen 

 under dark-ground hghting. They should be com- 

 pared with eggs of other kinds of diptera. The 

 larvse hatched from the eggs should also be examined, 

 not only as to their external form and members, but 

 also as to their internal organs. They are hatched 

 from the eggs about a couple of days after they are 

 laid ; they feed on refuse for about six days, then 

 change into the pupa stage. The perfect insects 



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