Fig. 1. Life cycle of Drosophila and constitution of the lymph gland.

(A) The fly undergoes four distinct phases of change that is commenced by the embryo which is formed after fertilization. The hatched embryo produces the first instar larva, which molts into second and then third instar larva, eventually forming a pupa. The pupa ecloses to the adult fly and the cycle repeats. (B) The lymph gland is the venue for definitive hematopoiesis. It comprises of four pairs of lobes and the primary lobe is divided into four regions: the posterior signaling center (PSC), the medullary zone (MZ), the intermediate zone (IZ), and the cortical zone (CZ). The prohemocytes of the MZ differentiate into plasmatocytes and crystal cells of the CZ. Lamellocytes are barely seen in healthy animals. The IZ contains differentiating prohemocytes that expresses both MZ and CZ markers.