a 
Prof, Bronté Gatenby’s Description of Dipterous Larva. 525 
lateral stigmata, but there is apparently a pair in the 
head region as in the Hristalis larva. 
The hind regions of this larva were sectioned in order to 
examine the truncate tubes. In Plate XVIII, fig. IV, there 
is drawn a transverse section of the body in ‘the region of 
the tubes; one of the latter is cut in longitudinal section, 
while two others, at DP, are just in the section. In fig. IV 
it will be noticed that the tube is hollow, from the pore 
upwards, to the place marked by the legend Tip. At this 
region the main tube is seen to be folded again to form an 
inner tube; to the inner tube are fixed some muscle bands 
at M; these are attached to the body-wall of the larva 
in the region of the tubes. Inspection of fig. IV at once 
shows that each tube is really arranged so as to be eversible 
by pressure of the fluid of the body, and the muscle at M 
functions in redrawing the tube when once everted. In 
fig. V the tube is diagrammatically represented as half 
everted, the tip (Tip in fig. IV) being now outside; in fig. VI 
the eversion is complete. The attachment of muscle is 
at MA. 
It was found that the hypoderm cells of the truncate 
tubes were very large and glandular. 
Probable Function of Eversible Truncate Organs.—In 
fig. II] is a diagrammatic drawing of a larva with its tracheal 
funnel above water taking in air; the eversible organs are 
shown protruded to their fullest extremity. There seems 
little doubt that these organs, connected as they are with 
the haemocoel, and everted by haemocoelic fluid pressure, 
serve as additional respiratory organs, when the larva is 
in water too deep to enable it to use its tracheal funnel. 
A less likely suggestion might be that the organs are used 
for climbing and adhering to water-weeds. 
Systematic Position of Larva.—Until the fly is bred from 
this larva, it will be impossible correctly to place it in its 
position, but in arrangement of legs, in the appearance of 
the integument, in the shape of the body, and in the 
tracheal apparatus, this larva shows undoubted affinities 
with the form Eristalis. 
[The following extracts from Farquharson’s letters con- 
firm Prof. Gatenby’s suggestion that the protrusible 
processes are respiratory in function.—E.B.P. | 
Dec. 12, 1917.—You will remember my telling you of 
the (?) Syrphid larva with the curious protrusible process, 
that I found in the decaying banana leaves in water. I 
TRANS. ENT, SOC. LOND. 1921.—PARTS III, IV. (JAN. 22) MM 
