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SANITARY ENTOMOLOGY 



part of each ring is much broadened and divided transversely by a narrow 

 smooth space. On segments 5 to 10 tliere is on eacli side behind a fusi- 

 form swoUen area pressing against the swollen ring of the next segment; 

 tliis area also lias spines. Tlie tip of the body shows on tlie dorsal part 

 a great cavity, in tlie bottom of which are the stigmal plates, each with 

 three straiglit slits, those of one sub-parallel to those of the other; 

 tliere is no button (fig. 30). Behind this cavity is a high, transverse, 

 spiny crest ; and the ventral part of the tip shows an area covered with 

 .spines bearing two rather widely separated, prominent, smooth tubercles. 

 Tlie upper edge of the tip sliows four small conical tubercles. 



Platk I\'. — Screw wiinii injury to u yearling calf. (Bishopp.) 



The larva of this insect is called the "screw-worm,"' and occurs in 

 sores and wounds of domestic animals and also in man. There are 

 various records of its presence in the cars and nose, or nasal cavities, 

 of people; in swellings near the nose; in a boil under the arm; under the 

 skin of a child ; and in the navel of a child. It is hardly a possible 

 factor in intestinal myiasis of man, and most of such recorded cases 

 probably belonged to some sjiecies of Sarcophaga whose larA'se are very 

 similar in apjDearance to those of the screw-worm. 



Sarcoph agidae 



The Sarcophagidae have two great hooks, and the posterior stigmal 

 plates have three slits as in Calliphora erytlirocepliaJa and Lucilia seri- 



