264 Prof. L. C. Miall and Mr, T. H. Taylor on the 
ventral arms. <A series of muscles, which are inserted 
into the dorsal wall of the pharynx, probably serve to 
dilate the cavity; when a live larva is placed in water 
charged with finely-powdered carmine the particles can 
be seen to enter the mouth at each contraction of the 
muscles. The cesophagus (fig. 3) passes between the 
cerebral ganglia. There is a cardiac chamber, with four 
czeca and an cesophageal valve. The stomach is long and 
convoluted. Two Malpighian tubules, each bifurcate, 
enter the beginning of the intestine. The whole alimen- 
tary canal is about five or six times as long as the body. 
The salivary-glands reach to the hinder-end of the body ; 
they are slightly dilated in front. Their ducts unite imto 
a single tube, which opens into the floor of the pharynx, 
perforating the median piece of the endocranium in order 
to do so; they show the usual cross-marking. It is hard 
to explain the large size of the salivary-glands, but as no 
pupal cocoon has to be made, their function is probably 
strictly alimentary. 
The Tracheal System.—A pair of longitudinal tracheal 
trunks run nearly the whole length of the larva (fig. 2). 
These trunks are connected with each other by transverse 
dorsal commissures, and give off segmental branches. 
Adjacent segmental branches are united by longitudinal 
connectives, from each of which arises a ventral trachea. 
There are ten pairs of closed spiracles, two thoracic and 
eight abdominal. The first and the last pairs occur re- 
spectively in the Ist thoracic and the 8th (spiracular) 
abdominal segment, and are placed near the mid-dorsal 
line ; the remaining spiracles are lateral in position, each 
being placed close behind one of the bands of segmental 
hooks. The anterior and posterior spiracles are often un- 
usually large in Dipterous larvee ; in the holly-fly they are 
closed like the rest in the young larva, but become 
functional in the later larval stages. The tracheal 
junctions which divide the longitudinal trunks into 
segmental systems are evident in the last larval stage. 
The Dorsal Vessel—The dorsal vessel or heart (fig. 3) is 
three-chambered, each chamber being provided with a 
pair of ostia. The fore-end of the dorsal vessel reaches 
the head-capsule and is attached to it, but actually opens 
into the thorax. 
The Fat-body.—Between the coiled strings of the fat- 
body are found bright refractive bodies of large size (fig. 4), 
