Haemopoiesis in Lepidoptera. II. The role of the haemopoietic organs

Abstract

Haemopoietic organs were found in association with the wing discs in 15 species of Lepidoptera examined. The organs were shown to contain small stem cells organized into islets which generate either oenocytoids or prohaemocytes–plasmatocytes. The great majority of islets comprised the latter, and there was evidence that prohaemocytes transformed into plasmatocytes. A decline in the size of the haemopoietic organs during the fifth instar indicated a major release of cells, and correlated with changes in the complement of circulating haemocytes.Total haemocyte counts were reduced in the posterior section of larvae ligatured in the middle, but differential counts showed a more marked decline in prohaemocytes and plasmatocytes than in other classes of haemocytes. Larvae with two or more ligatures usually showed higher prohaemocyte and plasmatocyte counts in the parts of the body that included the haemopoietic organs. Inclusion of the head and prothorax in such sections resulted in still higher counts of prohaemocytes and plasmatocytes as well as higher mitotic indices.The concept that there is a dual origin of haemocytes, from division of cells in circulation (granular and spherule cells) and from the haemopoietic organs (prohaemocytes, plasmatocytes, and oenocytoids) is presented.