50 E. H. STRICKLAND 
future as the oesophageal fold (0.f.) of which the end attached 
to the cardia is the apex and that at the flexure the base. The 
cells of the cardia are columnar in shape, and in stained prep- 
arations have a much greater affinity for such stains as haema- 
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Text fig. 1 Diagrammatic peritrophogen of a Simuliid larva. A, Section of 
peritrophogen in the normal position; 0, lumen of oesophagus; 0.f., oesophageal 
fold; i.e., reflected portion of the oesophagus; z, junction between the oesoph- 
agus and the midgut (stomenteron and mesenteron), c, cardia composed of 
enlarged mesenteric cells which secrete the peritrophic membrane p.m; ch, thick 
deposit of chitin on the basal half of the oesophageal fold, bearing stout 
bristles b; 1, ligament holding cardia in position around the oesophagus. 
B, Surface view of reflected portion of the oesophagus (oesophageal fold) showing 
imbricated tufts of downwardly directed bristles. C, Peritrophogen relaxed. 
D, Peritrophogen extended, showing the bristles, b, in contact with the freshly 
secreted peritrophic membrane. 
toxylin than the remainder of the mesenteron. As is the case 
with all the mesenteron cells they are glandular in function, 
and that they are very active is proved both by the quantity 
of secretion they produce and by their greatly enlarged nuclei. 
