Midgut
Mid gut in the larvae is mainly involved in digestion and absorption.
Histologically, a stratum of enteric epithelium, the outer ends of whose
cells rest upon a basement membrane lines the midgut. The latter is
followed by an inner layer of circular muscles and an outer layer of
longitudinal muscles. The midgut cell are of two types, columnar cells
and secretory or goblet cells. In addition regenerative cells replacing
the destroyed epithelial cells during moulting are also present. As
healthy larvae mid gut are rich in digestive activity, so the secretory
cells are seen normal and the absorptive cells are normal indicative of
good transport of absorbed material. Regenerative cells and their nuclei
are prominent. The basement membrane and musculature are normal (Fig.
3a).
However in the diseased silkworm, the epithelial layer of the midgut
lacked continuity. After infection, the hypertrophy was much more
pronounced and large vacuoles were formed in epithelial cells ofA. proylei midgut. Both secretory and absorptive cells were
hypertrophied. Absorptive cells are fully loaded indicating loss of its
absorption. The inter-cellular spaces widened to a great extent and
epithelial tissues detached from the basement membrane. Also bacterial
populations were seen with dark masses inside lumen indicative of its
infections corroding the epithelial layer (Fig. 3b).