THE EARLY STAGES OF CERT .UN WEST AFRICAN MOSQUITOS. 141 



The egg. — The eggs are laid on the under surfaces of the leaves of Pistia strat totes 

 in clusters or cushions about 2-3 mm. in diameter, containing about 150 eggs apiece. 

 Each egg is rounded at its attached end, but prolonged into a snout at its free end. 

 is dark brown in colour with the surface covered by a cellular reticulation, and measures 

 about 096 mm. in length and - 17 mm. in breadth at its widest part. At the blunt 

 end of the egg there is a layer of clear, colourless material to attach it to the surface 

 of the leaf. The pointed end projects freely and bears at its extremity the micropilar 

 apparatus consisting of a cap-like mass of clear, colourless material similar to that at 

 the rounded end. This cap is readily detached, revealing the presence of four blunt 

 processes at the end of the egg. 



The egg-masses lie on the under surfaces of the outer leaves. As the plant unfolds, 

 the leaves become nearly horizontal, and in this position the cushions of eggs come into 

 contact with the water, the pointed ends of the eggs being directed downwards. 

 When the larva hatches the egg breaks horizontally at its widest point, detaching a 

 cone-shaped piece about 37 mm. long consisting of the end of the egg and the micro- 

 pilar apparatus. This cone falls to the bottom of the water. The larva on escaping 

 also descends to the bottom and attaches itself to the root of a Pistia plant, selecting 

 a delicate rootlet and not the main tap-root as the older larvae do. 



Breeding place. — The larvae of Mansonioides africanus are found in pools and 

 swamps in which Pistia stratiotes is growing (see Plate I, fig. 1 ; II, fig. 1), but up to 

 the present we have not found them associated with any other water-plants. At 

 Accra we obtained specimens regularly from a particular pool from April to 

 November. In April and at the beginning of May the larvae were difficult to find, 

 in June they were very numerous, in July and August they diminished in numbers, 

 and in September and October they were again very few. They were most plentiful 

 therefore during the rainy season, which at Accra reaches its height in June. 



Ochlerotatus albocephalus, Theo. (fig. 2). 



The larva has a small and dark head, slightly more than half as wide as the thorax ; 

 the antennae are slender, curved and covered with spicules, the tuft is placed about 

 the middle and consists of a few subplumose hairs. The midfrontal hairs are multiple 

 (5-8) and are plumose ; the brushes are prominent, being composed of coarse hairs. 

 The eyes are large. The mental plate has a large median tooth and nine smaller teeth 

 on each side of it. 



The thoracic plumes are poorly developed, the constituent hairs being plumose. 

 The lateral abdominal hairs are multiple on the first segment, triple on the second, 

 and single on the remaining segments. The comb consists of 12-15 barbed spines 

 placed in an irregular row. The subsiphonal plume is composed of subplumose hairs, 

 the siphonal plume and the anal plume consisting of pubescent hairs, and there is a 

 single independent hair adjacent to the anal plume. The siphon is about three times 

 the diameter of its base ; the pecten comprises 9-11 spines, which become slightly 

 larger and are more widely separated distally ; a tuft of simple hairs is situated just 

 beyond the middle of the siphon (35-60). The anal segment is broader than it is long 

 (22 x 19) ; the anal papillae are almost equal in length, stout and with sharply 

 pointed ends, being longer than the anal segment (28 : 19). The beard is well 



