DEVELOPMENT IN MOSQUITO 311 
The movements, however, to the end of the ripening stage of the larva remain 
slow and very circumscribed. Generally the larve are found in extended 
position in the muscle fibers, these latter disintegrating into a fine granular sub- 
stance which serves as nourishment for the larve. A variable proportion of the 
larve die during this stage. 
When the larve have reached a certain size (given by various investigators as 
from 1.006 to 1.8 mm.) they leave the muscles and return to the general body- 
cavity. They now are very active and generally make their way to the anterior 
end of the mosquito, penetrating from the thorax into the head and from thence 
into the labium. Occasionally filarie go astray and get into the abdomen; they 
have also been found in the hollows within the legs and palpi. 
Lebredo gives the following synopsis of the filarial development within the 
mosquito : 
“1, The insect sucks the blood of a patient infected with filaria. 
“2. The embryo loses its sheath in the stomach of the mosquito, ecdysis. 
“3. Migration from the stomach to the thorax. This migration always takes 
place through the gastric wall, since both orifices of the gastric dilatation are 
completely closed when the stomach is full. The embryo leaves its sheath in the 
gastric contents or caught in the wall of the stomach, where it is left at the 
moment of exit. 
“4, The embryo rests in the thorax, and goes through the following trans- 
formations: 
“ (a) Narrowing and invagination of the tail. 
“ (6) Invagination continues and the embryo grows shorter and wider. 
“(c) Widening and shortening continue, and the invaginated portion forms 
a hyaline appendix. 
“(d) Period of growth and formation of the three lobes.” 
Then follows the escape of the fully developed larve into the general body- 
cavity. This is the period of its greatest activity which generally results in its 
gaining the interior of the labium. Then the larva awaits the next step in its 
evolution, the transfer to its vertebrate host. 
It has been frequently observed that the proportion of embryo filarie con- 
tained in the blood within the mosquito’s stomach is much greater than in the 
same quantity taken directly from the circulation. Various explanations have 
been offered, but Fiilleborn has shown that this difference is only an apparent 
one, being due to the dehydration of the blood within the mosquito’s stomach. 
At the same time this thickening of the blood makes it viscid and this serves, 
as it were, to hold the sheath when the embryo moullts, as it does at this time. 
The time necessary for the development of the larval filaria to its final active 
condition is variable. Manson first gave a period of seven days but no such rapid 
development has been observed by others and he himself admits that there may 
have been an error in his observation. James, in India, states the period to be 
from 12-14 days; Bancroft, in Australia, never saw them before the 16th or 
1%th day, and the period was extended to 35 days in cold weather. The govern- 
ing factor is evidently the temperature. Looss found that in the Egyptian 
winter some of the larvee were not fully developed until the 41st day after the 
