892 REPORT OF THE HARVARD AFRICAN EXPEDITION 
more and more deeply until the projecting palps rest on the skin, and after one 
or two sawing movements, the biting parts are extracted and re-inserted at 
another site. Once a satisfactory source of blood is secured, the feeding goes on 
uninterruptedly until the insect is replete. . . . In Experiment twenty-three, 
at Calabar, six flies were weighed immediately before and immediately after 
feeding. The increase of weight was respectively 0.059 gramme, 0.045 gramme, 
0.03 gramme, 0.03 gramme, 0.03 gramme, and 0.03 gramme. The pose in feed- 
ing is characteristic. The fly becomes rigid and tense, the wings are slightly 
extended, and the tip of the abdomen is tilted upwards. Shortly after the 
current of blood has begun to enter the gut, occasional spasmodic contractions 
of the abdominal segments take place, followed by the act of defecation. Grad- 
ually, as the abdomen distends, it begins to drop until finally it drags, and there 
may even be a droplet of fresh blood exuding from the posterior extremity. 
Once blood has been tasted by a willing fly, it may be forced to withdraw the bit- 
ing parts, but on release it will immediately re-insert them. When the biting 
parts are fully inserted, the labium is rucked up in folds like a loose stocking, 
with the labella flattened out on the skin. . . . The rate of sucking the blood 
varied considerably, sometimes five minutes or longer elapsing before the in- 
dividual is satisfied. Even although it may be barely able to crawl, it is always 
able, though in a heavy fashion, to wing its way to the side of the cage. Various 
preferences are shown by Chrysops. ‘They will more readily bite Africans than 
Europeans. They are also more ready to bite on a black area of a guinea-pig’s 
skin than on a white area. It was found, also, that they fed more readily on 
some of the black boys than on others.”’ 
In experiments with several hundreds of C. stlacea and C. dimidiata, only one 
fly laid eggs in captivity, although at the time (during June and July) female 
flies were present in very large numbers and for the most part carried unde- 
veloped eggs. In the one case observed, the eggs ‘‘ were deposited on a moist 
dead leaf lying on the surface of some swamp mud which had been placed in a 
tin at the bottom of the cage. These eggs were grayish white at first, latterly 
turning brown along their length and black at the tips. They were laid in 
a single layer, all upright, in an irregular mass, and they numbered about a 
hundred. After four days they had all hatched, and the young larvae had dis- 
appeared into the mud. A week later an attempt was made to recover them, 
but no trace could be found. Whether their cannibalistic tendencies accounted 
for this disappearance, or whether the swamp mud is an unsuitable medium must 
be left an-open question. Neither the ova nor the larvae differed in any way 
from those described for other species of Chrysops.”’ The Connals also found in 
the moisture gathered by the bases of the leaves of the ‘‘serew-pine” (Pandanus), 
which abounds on the river banks, very young larvae identical with those that 
hatched from the batch of eggs laid in captivity by a Chrysops as described above. 
Similar small larvae were also found in the cup of a small purple flower which 
grew in great profusion on the swampy river bank. 
Medical importance of Chrysops. — The only African human disease posi- 
tively known to be carried by tabanids is caused by a nematode worm, Loa loa 
