CHAPTER XXIX 



THE HEXAPODA 



Synonym — Remarks — Morphology — Internal anatomy — Life-history— Habits 

 —Enemies — Pathogenicity — Collection — Classification— References . 



Synonym — Insecta. — Arthropoda breathing by means of tracheae, 

 with antennae on the head, three pairs of legs, and usually two pairs 

 of wings on the thorax, which is composed of three segments. 

 Abdomen with generally nine apparent segments. 



Remarks. — The Hexapoda, or insects, are known to be of the 

 utmost importance in the spread of disease, for the researches of 

 Manson, Ross, Grassi, and others have shown that they are agents 

 in the propagation of the parasites of filariasis, malrria, and*other 

 diseases. 



Fig. 363. — Culicoides brucei, a Typical Dipterous Insect. 

 (From a photograph by J. J. Bell.) 



Morphology. — The body is distinctly divided into head, thorax, and abdo- 

 men. The head is composed of the fusion of about six segments, which are 

 the ocular, antennal, intercalary (probably homologous with the second 

 antennal segment of the Crustacea), mandibular, maxillary, and labial; but 

 whether the hypopharynx represents a seventh segment or not is doubtful. 

 The head carries, in addition to the eyes, four pairs of appendages, one for 

 each somite or segment, except the intercalary segment, which is pre-man- 

 dibular. These appendages are the antennae, the mandibles, the maxillae, 

 to which are attached palpi called the maxillary palps, and a second pair of 

 maxillae usually fused to form the lower lip or labium, which generally carries 

 a pair of labial palps. 



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