Haemocytology of the supraneural myeloid body in the sea lamprey during several phases of life cycle

Abstract

The supraneural myeloid body of the sea lamprey (Petromyzon marinus) was studied in the feeding adult, late spawning run adult, and metamorphosing ammocoete. The fatty nature of the tissue was established by histochemical staining and electron microscopy. The presence of the fat cells and the actively differentiating blood cells evinced its similarity to the bone marrow in higher animals, thereby suggesting a phylogenetic affinity. In the late spawning run lampreys, the tissue was found to be almost empty of blood cells, leaving empty spaces within the stromal skeleton. In the feeding adult tissue, the various blood cell types differentiated from precursor cells have been identified. Megakaryoblasts possibly representing early phases of the cell type were observed only in the transforming (macrophthalmia stage) and adult lampreys. A marked active development of the tissue in the ammocoete was seen only at the fourth stage of the metamorphosing ammocoete immediately before macrophthalmia. At the macrophthalmia stage, the haematopoietic activity in the tissue increased substantially.