LARVA OF ANOPHELES 91 
extends a rather thick layer of plasma with scattered nuclei. Each tube contains 
a tracheal trunk which sends off numerous branches to the sides; the tube is 
hollow and represents a blood sinus. The tracheal gills are connected with 
muscles and thereby serve as closing apparatus of the colon. While ordinarily 
they are disposed wreath-like around the anus, they can, by muscular exertion, 
fold together into the form of a wedge.” 
MODIFICATIONS OF LARVAL STRUCTURE. 
Other mosquito larvae present essentially the same structures as the larva of 
Culez, although variously modified. With a good knowledge of the Culex larva 
there should be no difficulty in understanding the structures of other larve. 
Many of these differences are brought out in the systematic part of this work, 
others may be briefly noted here. 
The most striking difference is presented by the larva of Anopheles in the 
absence of a respiratory tube and its adaptation to the surface-feeding habit. 
Aside from its adaptation to habits the larva ofAnopheles is primitive, as is in- 
dicated by many of its structures. The larva when at the surface of the water 
is still submerged ; it is suspended from the surface-film by means of the struc- 
tures surrounding the spiracular openings on the eighth segment and by the 
“ stellate tufts,” situated on the dorsal surface of the body. These stellate tufts 
are little rosettes of leaf-like hairs with a common stem which spread out upon 
the surface of the water. The stellate tufts are situated dorsally in pairs on 
certain of the abdominal segments, and in some Old World species also upon 
the thorax. 
The head of the Anopheles larva is narrower and more elongate than in other 
mosquito larve. The elongate appearance is due to the fact that the dorsal 
region of the head is well produced between the antenne. The “mouth- 
brushes” are more compact and closer together than in the Culex larva and 
their mechanism is simpler. The primitive character of the larva is indicated by 
the comparatively simple mandibles, the large, square maxille and the very 
large, nearly independent, maxillary palpi. These latter are not inserted in a 
plane with the maxille but hinge farther back upon a part of the ridge of the 
hypocranium, which is interrupted at this point. 
The trachesz open separately through spiracles on the eighth segment. An- 
other primitive character of the Anopheles larva is the presence of chitinous 
dorsal plates on the abdominal segments. These are small and transverse, situ- 
ated at the anterior margin on all but the ninth segment. This last has a large 
saddle-shaped dorsal plate. 
The “lateral comb” of scales of the eighth segment of the Culex larva is 
represented by two large chitinous plates, situated laterally near the posterior 
extremity of the segment. These are attached to the sides of the segment by 
their upper margins and project downward and slightly outward; the lower 
margin is produced into a series of long irregular teeth, which point backward. 
The two plates are connected posteriorly by a chitinous strip in continuation of 
the thickened upper margins. These structures serve as a support to the 
mechanism surrounding the spiracles. In the first stage larva of Anopheles 
