hungerford: anatomy of simulium vittatum. 379 



indistinctly as dark dots on the gray surface of the insect but 

 show plainly in specimen treated with caustic potash. They 

 are not functional in the larva and pupa, their work being 

 taken over by the blood gills in the larva and by the cuticular 

 gills in the pupa. 



Taylor, '02, finds that the general scheme of tracheation is, 

 however, about the same in the larva and pupa stages as in the 

 adult, save for method by which the air is brought into the 

 system mentioned above. His studies were upon Simulium 

 latipes, and in his researches he records but five abdominal 

 spiracle branches, failing to find the one in the second segment, 

 which he thinks, however, must exist in view of the fact that 

 the cast pupal skin shows an attached remnant of such a 

 branch. He also infers that one exists in the first in some 

 vestigial form, but I am unable to confirm this. 



In the thorax there is a tendency of the tracheal branches 

 to be dilated, and the fact that there are several large trunks 

 or branches originating at the metathoracic spiracle and ex- 

 tending forward in different planes of the thorax makes it 

 difficult to distinguish the main trunk from the others. In 

 fact, if my interpretation is not incorrect, the main trunk is 

 much smaller than the very large branches that are sent off. 

 (See Fig. 5, PI. XLIV.) This main trunk extends from the 

 metathoracic spiracle underneath the large oblique thoracic 

 muscles and runs along dorsolaterally to the fore gut, turning 

 up before the first oblique muscle to meet the other branches ex- 

 tending from the mesothoracic spiracle. It then continues to 

 the head where it breaks into many branches. These main 

 trunks are connected in the thorax by one prominent com- 

 missure arising from the caudal end of the anterior third and 

 looping up over the alimentary canal to the top of the second 

 longitudinal muscles and thence back in the same plane be- 

 tween the right and left longitudinal thoracic muscles, joining 

 the corresponding trunk on the other side. From the meta- 

 thoracic spiracle there arise the following branches: one ex- 

 tending dorso-cephalad laterally to the main muscles of the 

 thorax for some distance, then narrowing suddenly, it turns in 

 under or between the outer oblique muscles, four and five, and 

 gives off one small branch; another has the same general di- 

 rection but lies in the plane between second oblique and first 

 longitudinal and extends to the thoracic wall, where it turns 

 ventro-cephalad at right angles and drops beneath the sixth 



