a2 E. H. STRICKLAND 
that when in this condition it is very ductile. Plate 6, figure 8 
shows that the portion of the cardia which secretes the peritro- 
phic membrane is normally distant from the orifice of the proven- 
triculus, and the question arises as to how the secretion passes 
backward, as a regular film, to the point where it can first come 
in contact with the food, to form, when hardened, a continuous 
membrane which will entirely invest it during its backward pas- 
sage through the alimentary tract. There is, in every species 
of Simulium which I have as yet examined, a structure peculiarly 
fitted to accomplish this, and this structure does not appear to have 
been seen in any other insect. I failed to locate it in Chirono- 
mus but have not examined the larvae of other allied families. 
In the accounts and figures of the cardia and peritrophic mem- 
brane of Culicidae by Thompson (’05) and [mms (’07) this 
structure is neither mentioned nor illustrated, so it is probably 
not to be found in the larvae of this family. It will be remem- 
bered that, as previously stated, the internal secreting surface 
of the cardia is faced by the internal surface of the oesophageal 
fold. The latter, being of ectodermal origin, is lined with chitin, 
and that lining the basal or posterior half of the fold is very 
much thickened, so as to be quite rigid (text fig. 1, A). It isalso 
beset with strong, backwardly projecting, black bristles, placed 
in radiating tufts, which are arranged in an imbricated manner 
over the entire surface of this reinforced area (text fig. 1, B). The 
chitin lining the apical or anterior half of the fold is much reduced 
and hardly discernable in most larvae. The epithelial cells which 
secrete this small quantity of chitin are themselves also very 
small. This renders the basal half of the oesophageal fold, which 
normally lies opposite the functionless portion of the cardia, 
very rigid, and the apical half, which faces the secreting cells of 
the cardia, very flexible. The cardia is held in place around 
the proventriculus by an elastic ligament (l.) formed of connective 
tissue, which is attached to its anterior extremity, and to the 
external wall of the stomenteron. This ligament is capable of 
great extension and enables the cardia to be drawn backwards 
and forwards over the chitinous surface of the oesophageal fold. 
These movements were actually observed to take place in a liy- 
