THE SCREW-WORM 359 



for man. It forms tumors under the skin which it is thought may reach this location 

 by proceeding in some way from the alimentary canal. 



In Hypoderma the arista is bare while in Dermatobia the upper border is plumose. 



MYIASES 



Ver Macaque. The best known of these myiases is that due to the 

 larva of a gadfly, Dermatobia cyaniventris. 



The larva is at first club-shaped and in this stage is called ver macaque. Later on 

 it becomes worm-shaped and is then called torcel in Venezuela or berne in Brazil. 

 The natives of most of the countries where the infection is found have called the 

 larvae "mosquito worms" or "gusano de zancudo" and they have even incriminated 

 large mosquitoes belonging to the genus Psorophora as being responsible for the 

 infections. 



Surcouf has noted that these fly larvae have been found cemented to mosquitoes 

 of the genus Janthinosoma by a glue-like substance. These mosquitoes are vicious 

 biters and evidently the young larvae escape from the eggs attached to the mosquito 

 and enter the wound made by the biting parts of the mosquito. Some have thought 

 that D. cyaniventris deposits its eggs in a glue-like material on the leaves of plants 

 and that they stick to mosquitoes flying about such plants. From the facts that 

 these eggs apparently only become attached to this particular mosquito and further 

 in that the eggs are attached in a constant manner with the hatching end outward it 

 would seem that the mother fly must in some way seize the mosquito and deposit her 

 eggs on it. As the larva grows in the subcutaneous tissues of man or other animals 

 a tumor-like swelling develops with a central orifice, toward which the posterior 

 extremity of the larva points and through which it takes air into its spiracles. 



The swelling somewhat resembles a blind boil and may be as large as a pigeon's 

 egg- 



These gadfly boils tend to break down and discharge a sero-purulent fluid and it is 

 supposed that the larva, when mature, escapes as a result of the disintegration of the 

 tumor. 



In Brazil they make tobacco juice applications which cause the larva to protrude 

 and then squeeze it out. The injection of a little chloroform into the larva with a 

 hypodermic syringe, prior to its extraction with a forceps, makes the process less 

 painful. 



The Screw-worm. This is the larva of a blue-bottle fly, Chrysomyia 

 macellaria, which differs from the common blue-bottle fly, Lucilia, 

 by having three black lines on scutum, 



This muscid fly lays 200 to 300 eggs in wounds or orifices having offensive dis- 

 charges, as from nose, ears, etc. The larvae burrow into the adjacent tissues and 

 cause frightful destruction of all soft parts. The mature larvae are a little more 

 than % inch long and have circlets of spines around each of the 1 2 segments. 



This infection is especially common in tropical and subtropical America and is 

 important in animals as well as man. 



