ORGANIZATION OF HEMATOPOIETIC-TISSUE IN THE INTERMOLT LOBSTER, HOMARUS-AMERICANUS

Hematopoiesis in the American lobster Homarus americanus, as in most d ecapod crustaceans, occurs in a thin tissue covering the dorsal surfac e of the foregut. This tissue is composed of loosely attached, ovoid l obules containing the hematopoietic precursors and maturing hemocytes. Release of hemocytes into the dorsal hemocoel is accomplished by rupt ure of a portion of the connective tissue capsule covering the lobule. Cross sections of the lobules contain between 6 and 40 hematopoietic cells, of which approximately 90% constitute stages in granulocyte mat uration and 10% are intermediates in hyaline cell maturation. Hematopo ietic precursors in these two lines are similar to those recently desc ribed in a penaeid shrimp Sicyonia ingentis. The mitotic rate averaged 5.1 % (range = 0.7% to 15.8%) in intermolt lobsters, 90% comprised gr anulocyte precursors.