The fat body of insects is in the form of loose masses of cells which are mesodermal in
origin. Membraneous connective tissue sacs enclose these cell clusters. they look like
aggregates of blood cells. They freely project into the haemocoele and are penetrated by a
dense network of fine tracheoles.
The major part of the fat body is built up of cell called trophocytes. In the young
animal the trophocyte is small, comparatively clear and with large, rounded nucleus. In
due course, the cell develops cytoplasmic vacuoles and becomes enlaged due to deposits
of glycogen,fats, or protein. At metamorphosis, albuminoid granules appear in the cyto-
lipids in Anthrenus. Droplets of the enzyme lipase are associated with each droplet of fat.
The trophocytes get loose and float about like haemocytes in Aleyrodes and in aquatic
bug blood cells contribute to the formation of trophocytes. It is possible that there is a
relationship between trophocytes and haemocytes.
Functionally, trophocytes are stored house of food material. Fat is the chief component.
Glycogen and protein also are stored in them. Protein storage is marked in animals which
hibernate. Nearly 33% of the weight of a mature Apis larva is due to trophocytes. The
reserves in trophocytes are drawn up under conditions of starvation or inactivity. They
contribute also to the development of eggs. The presence of lipase in fat droplets within
cells indicate that hydrolysis into fatty acids and glycerol also occurs within this organ.
They then get transported to respiring tissues for utilisation.