522 
H D-K (410915 p:507) state as. follows: Alr' tube about. twice sas 
long as wide, the basal part broad and strongly convex, the apical 
portion attenuated, anterior apical third channeled; two filamentous 
hairs arise from near base of attenuated portion, the anterior wall 
of which is thick and finely dentate, ending in terminal hooks; 
no pecten, a single pair of hair tufts at basal third." That of 
titillans is decribed as follows H. D. K. (1915 p. 519): "Air tube 
short, conical, the apical portion attenuated, bearing a tuft of four 
hairs on each side near the middle and a pair of filaments at base 
of apical projection; this consists of two thick lamellæ with a group 
of hooks at the tip and two or three stout teeth on the anterior 
aspect medially.” As far as I can see, none of the two descrip- 
tions are in full accordance with the sipho of M. Richardii. 
Fhetracheal system. 
If we regard a living larva (fig. 35) the attention will immediately 
be attracted by the tracheal system. Between the thorax and the 
first abdominal segment two 
large bladders' are situated ; 
the half part of the bladders 
reaches into the thorax and 
occupies a great deal of its 
cavity. At the first glanceé 
these bladders resemble thosé 
of the Corethra-larva, but 
differ from these in being 
connected with the two main 
tracheæ by two smaller, right- 
angularly curved tracheæ. The 
Fig. 35, Microphoto of living larva to show point of insertion is situated 
the flattened tracheal stems and the two large Ea 
bladders (the white spots between thorax ind at the limit between the thorax 
valten mu nne and the abdomen. Fig. 36 
illustrates the description. It will be seen that the front parts of 
the bladders are furnished with some few short, slender tracheæ, 
and that the two large longitudinal stems of the body are broad, 
band-like in the thorax and the first part of the abdomen. In fact, 
these main tracheæ are double, consisting of two associated trunks, 
still indicated by a longitudinal fold; in the thorax each of thé 
two trunks is further divided by another longitudinal fold. Thé 
