48 E. H. STRICKLAND 
collected were on leaves which I placed in the water without 
touching the pupae, so as to prevent any possible damage. Only 
in three cases, however, in all of which the pupa was almost 
mature, was development completed, and in all of these the flv 
failed to reach the surface of the water without wetting its wings. 
Mr. A. H. Jennings of the Bureau of Entomology, to whom I 
mentioned this fact, suggested that it might be due to the ina- 
bility of the pupa to extract sufficient oxygen from the stagnant 
water to envelop the contained fly entirely and thus protect it 
from the water upon its emergence. 
a. The cephalic fans 
The cephalic fans of Simulium larvae (pl. 5, fig. 1 a) are ex- 
tremely specialised organs and are wonderfully suited to enable 
the larvae to obtain food from the water in a vertical position, 
thus avoiding the necessity of searching for nutriment in the 
bed of the stream. In the adult larva of Simulium bracteatum 
they are composed of about fifty curved rakes, which, when the 
fans are extended, form two very efficient bowl-shaped strainers, 
capable of collecting a large quantity of small food-particles from 
the water as it flows through the small spaces between the cilia 
of the rakes. In very young larvae, however, these organs are — 
far less completely developed. . In a larva measuring only some 
0.75 mm. in length they are represented by only about ten widely 
separated rakes instead of the complete number of about fifty. 
In two very minute larvae not a single rake was present. Whether 
this is an abnormal condition or not I am unable to state, but 
in both cases the alimentary tract was filled with food. I have 
dissected and sectioned many eggs from different masses, but 
have been unable to find any in sufficiently advanced stages to 
show whether the fans are normally formed in the embryo or 
not. It is a significant fact, however, that neither in the work 
of Kélliker (42), nor in that of Metschnikow (’66), which rep- 
resent the only embryological studies of these insects, are the 
cephalic fans either figured or mentioned. It would seem, there- 
fore, that the youngest larvae have to obtain their food by pick- 
