242 REPORT OF THE HARVARD AFRICAN EXPEDITION 
stream correspond in all respects to Simulium damnosum. It seems exceedingly 
probable that the larvae and pupae are also of this species. However, Bequaert’s 
description does not coincide with that previously given by other authors and it 
would appear as though his description of the larvae and pupae of Simuliwm dam- 
nosum given in this Report is the correct one. 
Simulium damnosum is widely distributed in parts of the equatorial regions 
of Africa. In places it is known as the Jinja fly, and in Uganda it is called 

No. 178. — Form undergoing ecdysis No. 179. — Advanced thoracic form 
Photomicrographs of larval forms of Onchocerca volvulus in Simulium damnosum 
mbwa. In the Congo we found it particularly about Leopoldville. These flies 
bite particularly on the bare legs of the natives, and many of them rested on 
the backs of our brown leather leggins or boots. 
On several different occasions, adult flies were collected from the banks 
of this stream and dissected, but no filarial larvae were ever found in them. 
However, later, in Simulium damnosum collected when biting near the village and 
about our camp, the filarial embryos were found both in the gut and later in the 
thorax of the flies. In one fly caught about our improvised laboratory, five motile 
larvae were found in the thoracic segment of the insect and three in the abdomi- 
nal one. In another fly, also caught in this laboratory, at least five larvae 
were found in the thoracic muscles. The thoracic forms are not so motile as 
those seen in the gut. One of their characteristics is that they have a move- 
ment of the caudal extremity without changing position on the slide. In the 
thoracic muscles they have also increased in width and the caudal appendage is 
peculiarly spine-like, and either straight or curved (No. 179). The parasite 
greatly increases in length in this region, to three times its former size. Our 
