112 
Anopheles Maculipennis 
those segments. Each ganglion of the ventral nerve cord gives off a pair 
of principal nerves to its segment, and they pass outwards between 
the longitudinal sternal muscles and the integument .(Figs. 3 and 22). 
A system of transverse nerves is also present; a fine nerve runs along 
the junction between each pair of segments above the abdominal nerve 
cord, and each is connected with the ventral ganglia by means of median 
nerves. Owing to lack of opportunity at present descriptions of this 
and several other important features in the Anopheles larva are post¬ 
poned for a future paper. 
Circulatory System. 
The heart is a muscular tube which extends from the posterior 
margin of the eighth abdominal segment, and jDasses forwards through the 
thorax into the head, where it terminates in the neighbourhood of the 
brain. In the region of the abdomen it consists of a series of consecu¬ 
tive chambers, each being provided with a pair of lateral ostia or inlets 
and, associated with them, are the alary muscles. In the thorax the 
heart is much reduced in diameter, there are no alary muscles, and it 
forms a narrow well-defined tube which is usually termed in Insects the 
aorta. The latter extends forwards through the occipital foramen and 
becomes enclosed just behind the brain in an irregular mass of tissue 
which forms a kind of supporting collar or anneau de soutien. 
The abdominal portion of the heart consists of a series of eight 
successive chambers and it expands somewhat at its posterior extremity, 
the last chamber forming a slight bulbous enlargement. The intimate 
connection that exists between the tracheal system and the terminal 
region of the heart has already been referred to ( Journ . of Hygiene, 
1907, p. 311, PL V). 
The structure of the wall of the heart is entirely muscular, and 
consists of flattened cells whose protoplasm mainly takes the form of 
striated fibrillae, which are disposed more or less parallel to one another 
(Fig. 30). Both externally and inteimally, the heart is invested by a 
delicate transparent membrane which is to be regarded as the sar- 
colemma of the muscle cells (Fig. 29). The striated fibres encircle the 
heart posteriorly in a slightly oblique manner, but further forwards 
they become arranged in a longitudinal direction so that their cut ends 
are only visible in transverse section (Fig. 15). The nuclei of the cells 
are situated laterally and form noticeable bulgings in the heart wall 
