i6 
REl'ORT OF THE MALARIA EXPEDITION. 
language), while those of Culex are generally plain. There are exceptions to both these 
statements ; but the rule holds good in Freetown, and also, according to the observations of one of 
us, in India. 
The eggs of Anopheles have a peculiar boat-like shape, while those of Culex are oval or 
lanccolar, 
(2.) Larva. — Here too, very fortunately, there is a marked difference. The trachea of 
Culex terminate in a long buoy-like breathing tube which projects, sometimes to a great length, 
above the tail fins. On the other hand, the tracheae of Anopheles merely terminate just above the 
tail fins, in two apertures which are nearly flush with the back. 
Apparently owing to these facts, the attitude also of the larvae of the two genera is 
different : those of Culex^ when at rest, hang suspended head downwards by the attachment of 
their breathing tube to the surface of the water ; those of Anopheles float flat on the surface like 
sticks. 
When disturbed, Culex larvae immediately leave the surface and wriggle to the bottom of 
the water, floating up again a few moments afterwards by the buoyancy of their air-tube. The 
movements of Anopheles larvae are quite different. They move on the surface of the water with a 
few peculiar backward jerks, followed by a pause ; and sink to the bottom only when much 
molested. 
Lastly, Culex larvae live mostly in artificial collections of water, while Anopheles larvae 
prefer natural collections — a point, however, which requires special consideration. 
12. Breeding Places of Culex. - In Freetown, as in all collections of houses, there are 
to be found in the vicinity of human dwellings innumerable tubs, pots-, shards, etc., in which a 
little rain water or household slop water collects. In almost all such in Freetown — tubs, pots, 
buckets, cisterns, empty oil-tins, biscuit-tins, sardine-tins, gourds, flower-pots, broken pottery, 
crockery, and bottles, even in unbroken bottles thrown uncorked on heaps of refuse — we found 
Culex larva;. The only condition necessary to their existence appeared to be an ounce or more of 
water preserved from desiccation or leakage. Occasionally, also, the larvae were found in hollows 
in rocks, pools by the side of roads, and even in small runnels of water. Very numerous larvae of 
a gnat of the 6^. tceniatus type were observed in hollows in rocks on the top of Signal Hill (400 
feet), near the Signal Station (occupied) ; also some of the same larvae, in a hole in rock hundreds 
of )'ards from human habitations. 
Similar facts have been always observed by one of us in India. Drains, ditches, and small 
ponds must be added to the haunts of Culex larvs ; but, as a rule, vessels of water near houses 
appear to be their favourite habitations. 
13. Breeding Places of Anopheles. — We made a very elaborate search in Freetown 
for Anopheles larvae. Every part of the town shown in a map which was given to us was carefully 
examined ; and wherever a breeding place of Anopheles was observed it was entered on the map 
{Map II. \ 
