110 Anopheles Maculipennis 
tion, and a long rudiment of the future reproductive duct has been 
developed. It extends backwards nearly to the posterior border of the 
seventh abdominal segment (Fig. 11). The duct, at first, takes the form 
of a solid cellular strand, but becomes hollowed out at a later period. 
The terminal filament is embedded in the visceral layer of the fat-body 
(Fig. 13 «.). 
In a larva measuring 6'75 mm. long, the female rudiment occupies 
both the fifth and sixth abdominal segments (Fig. 12), it is more 
elongated than that of the male of a corresponding age, and shows 
marked differences in its histological characters. In both sexes the 
genital rudiment is invested exteriorly by an apparently structureless 
tunic, and in the later larval periods the central mass of the organ is 
seen to consist of a number of small cell-clusters, separated from one 
another by a small amount of interstitial tissue. It is from these cell- 
clusters that the spennospores in the case of the male and the ovarian 
follicles in the female become developed (Figs. 12 and 13 6.). 
But little is known concerning the development of the reproductive 
organs of Diptera, or other Insecta, during the larval period. Among 
the Brachycera, some observations are given by Weismann (1864, p. 205, 
Taf. XIV, Figs. 67—72) in the case of Musca vomitoria and Sarcophaga 
carnaria. In the Nemocera, the larval gonads are best known for 
Chironomus (Balbiani, 1885, p. 527, and Miall and Hammond, 1900, 
p. 135), and Corethra (Weismann, 1866, p. 99, Taf. VI). Miall and 
Shelford also give some brief notes on those of Phalacrocera (1897, 
p. 35), and Lecaillon for the female rudiments in Gulex (1900, p. 96). 
In Chironomus and Cecidomyia it is known that the sexual germs 
develop at an extremely early period in the embryonic life, being 
formed as polar cells at the surface of the egg before the blastoderm has 
been developed. How far this precocious development of the sexual 
germs is at all general among Insects is at present unknown. 
The Nervous System. 
The nervous system consists of the brain or cerebral ganglia, and a 
ventral nerve chain of twelve ganglia (Fig. 23). 
The brain alters considerably in shape and in the relations of the 
parts, during the growth of the larva, especially with regard to the optic 
and antennary lobes. In the very young larva, the optic lobe is 
separated from the antennal lobe by a wider area than is the case in 
