(A) Blood cells in a healthy larva: plasmatocytes are in green and crystal cells are in magenta; white indicates the presence of both types of cell. Sessile blood cells of the first generation form a pattern of patches under the skin. Second generation blood cells accumulate in the ‘lymph glands’ (which are not related to vertebrate lymph glands in structure or function). Circulating blood cells do not give sharp images. (B) Large numbers of lamellocytes (red) accumulate in larvae infected by parasitoid wasp eggs, attaching to the eggs and other parts of the larva. The sessile blood cells become dispersed, the primary lobes of the lymph glands release their contents, and the secondary lobes enlarge.