294 Mr limns, Notes on the Structure and Behaviour of 
ment and it is probable that they function as accessory respiratory 
organs. 
The heart is a muscular tube which extends from the posterior 
margin of the eighth abdominal segment and passes 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 consecutive chambers each being provided 
with a pair of lateral ostia or inlets and associated with the latter 
are the alary muscles. In the thorax the heart is much reduced 
in diameter, there being 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 nervous system consists of the brain or cerebral ganglia 
and a ventral nerve chain of twelve ganglia. The latter comprise 
the sub-oesophageal ganglion, three thoracic ganglia and a series 
of eight ganglia to the abdomen. The ganglia of the last two 
segments are fused together into a ganglionic mass situated in 
the eighth abdominal segment. 
The muscular system was dealt with in some detail and 
special attention was given to the jaw muscles, the muscles of the 
spiracular skeleton and those of the ventral tail fin. 
The fat body is almost entirely confined to the thorax and the 
first seven abdominal segments. It consists of a parietal layer 
situated just beneath the integument, a visceral layer lining the 
body cavity and lying between the longitudinal muscles and the 
gut-wall, and a peritracheal layer which invests some of the 
principal tracheal trunks. The limits of distribution of each of 
these divisions vary according to the age of the larvae, and a 
certain amount of individual variation is also noticeable among 
specimens of as nearly as possible the same age. 
. GEnocytes are present and well developed, and belong to two 
varieties the large and the small. The large oenocytes are 
segmentally arranged in clusters, and are present in each of the 
first seven abdominal segments, but were not observed in the 
eighth or ninth segments, and are likewise absent from the thorax. 
The small oenocytes are very numerous and, moreover, have no 
definite arrangement. They occur just beneath the hypodermis 
in the neighbourhood of each group of the larger oenocytes and 
are mainly situated anterior to the latter, but they also occur in 
some numbers along the floor of each segment, on either side of 
the nerve cord. They occur in the first seven segments, a few are 
also present in the eighth, but none were to be discovered in 
the last segment. The imaginal buds are well developed and 
