312 
the sipho of Mansonia (figs. 23 and 27), we will understand the 
transformations which have taken place. 
Among the five normal flaps of a Culex-sipho the two largest, 
the ventral ones, are homologous with the ventral pair of the two 
pair of long pieces in the Mansonia tube. These two pieces carry 
a bunch of bristles (a), and so do the two ventral flaps in the 
Culex. We see, further, that the posterior edge of these flaps is 
serrated in the Culeæ. In all the hitherto known mosquito larvæ 
the two next lateral pieces are more hyaline and not so strongly 
chitinized; interiorly they are furnished with a peculiar chitin bow 
(c1), carrying a short bristle on its apex (fig. 29c). They may possibly 
be homologized with the two dorsal lateral parts (g) in the outer tube 
of Mansonia, Still I am more inclined to homologize them with the 
two peculiar hyaline cushions carrying the two long curved climbing- 
bristles in Mansonia. According to my opinion, the single dorsal 
. piece in the Culex is identical with the single dorsal piece pro- 
vided with sawteeth in the tube of the Mansonia (m). According 
to the use of the extreme part of the sipho as a piercing organ, 
this piece has been displaced to the inner side of the tube and 
united with the inner tube; it is therefore best described in con- 
nection with this. The single, short, lancet-shaped piece (h) on 
the ventral side is the only new addition which has no parallel in 
the Culex. Another difference is the fine hyaline chitin between 
the pieces prolonged together with these, and the fact that the apex 
of the tube carries a number of thorns. 
It is a wellknown fact, that the two main tracheæ in a common 
mosquito larva run into the sipho, terminating by the spiracles on 
its apex. According to previous authors as well as to H.D. K. there 
are two spiracles. They open in the bottom of the cup-shaped 
impression on the edges of which the closing apparatus is placed. 
As stated by Raschke the two tracheal trunks lose their spiral- 
thread structure towards the end and are transformed into firm 
cylindrical cups, provided with a considerable constriction at their 
bases. This is clearly shown in fig. 30. Between the two trunks 
there is a stiff. hollow chitinous rod, the "stirrup-shaped piece" of 
H. D. K., which is united with the two cups at their point of 
meeting, and partake in the limitation of the hollow space thus 
formed; accordingly this hollow space is formed by the cups on 
