8 ARTHROPODS 



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thorax short; proboscis short, thick, generally retractile; small or 

 medium insects; larvae, maggots, usually scavengers. 



Ortalidae. Gallflies. 



Abdomen pointed ; wings generally spotted or banded ; front 

 prominent; mouth wide; proboscis thick; larvae bore in stems of 

 herbs. 



Hippoboscidae. Sheep ticks. 



Head flattened, sunken thorax; wingless, degraded, parasitic 

 forms. 



THE DRAGON FLY 



Libellula sp. 



General Characteristics. — What is the most striking 

 difference between this insect and the others studied? How 

 are the wings held? Is there an unusual freedom of the 

 head? Of what value is it? Make a diagram showing the 

 longitudinal and lateral axes. 



The Head. — How much of the head is devoted to the 

 eyes? The eyes of some species of dragon fly are thought 

 to have as many as twelve thousand five hundred facets 

 in each eye. Are ocelli present? Do you find antennae? 

 What accounts for the condition in which you find the an- 

 tennae ? 



Draw front of head (X2). 



Beginning with the labrum find all the mouth parts as in 

 the grasshopper, and remove them with forceps. 



Draw mouth parts (X4)- 



The Thorax. — (i) Study the attachment of the legs 

 to the body. How many segments in the legs? Of what 

 use are the legs of a dragon fly ? 



