THE FLIES THAT CAUSE MYIASIS IN MAN 17 



MORPHOLOGY 

 ADULT 



The body of the adult fly is divided into three parts — head, thorax, 

 and abdomen. Each division is composed of three or more segments, 

 although in the head the segments are fused and their exact number 

 has not definitely been settled. The term "segment*' may be applied 

 to the divisions of the body as a whole or to those of an appendage, 

 such as an antenna, a palpus, or a tarsus. When a segment, as in the 

 antenna, is subdivided, or when segments have partially fused so as to 

 lose their identity though retaining a semblance of it, the term 

 "annulus" is applied to the subdivision. 



The integument is more or less hardened by the deposition of some 

 substances of uncertain chemical nature. This hardening is often 

 called chitinization. although it has been shown that this term is 

 erroneous, chitin itself being not particularly hard; sclerotization is 

 the proper term. Sclerotization takes place in definite areas which 

 are called sclerites. The terms applied to certain sclerites and to 

 bristles located on them are in considerable use in the taxonomy of the 

 muscoids. 



The body of a fly or of its larva is very rarely completely bare. 

 Several terms applied to the vestiture need definition. Pubescence is 

 very short, fine, downy hair that often escapes notice in casual exam- 

 inations: the usual hairy covering of the adult consists of pile, which 

 is soft and rather dense, and setulae. which are coarser. The large, 

 coarse, hairlike structures, which tend to assume definite patterns of 

 distribution and which are very important in the adult taxonomy, are 

 the bristles (macrochaetae). Color patterns in the adult may be due 

 to pigments in the integument, but often they are derived from dense 

 pilose coverings. Another common source of color is the pollen, a 

 fine dustlike substance which may cover parts of the integument and 

 give it a bloom, often vivid enough to conceal the ground color. 



Unfortunately, separate systems of terminology have come into 

 use in taxonomy and morphology, with the result that often a term 

 used in description does not refer to the real morphological equivalent. 

 In order to avoid complications, the terminology of the taxonomists is 

 strictly adhered to. 



The head (fig. 1) offers a considerable number of characters of 

 taxonomic importance. From an anterior view, the part between the 

 eyes is known as the front above the antennae and as the face between 

 the antennae and the oral margin. The upper part of the front is 

 known as the vertex; in its center there is a well-marked sclerite. the 

 ocellar triangle (of), on which the three ocelli (oc) are situated. 

 In the higher flies the front is divided longitudinally into three 

 regions. The median region is the frontalia or frontal vitta (frl) ; to 

 each side of it is a parafrontal (pfrl) which is continuous with the 

 similarly located parafacial (pfcl) of the face. The parafrontal and 

 parafacial together form the ocular orbit, a term which is also used 

 in the lower flies, in which the parafrOntals and parafacials are not 

 differentiated, to denote a similarly located region. In the higher 

 muscoids the median region of the face is separated from each para- 

 facial by the ridgelike facial (fcl) and a suture, and is divided into 



752113 "— 48 2 



