SEGMENTAL PODOCYTIC EXCRETORY GLANDS IN THE THORAX OF HUTCHINSONIELLA-MACRACANTHA (CEPHALOCARIDA)

All thoracic limbs of Hutchinsoniella except for the ninth contain a s mall gland composed entirely of podocytes. At the periphery of the gla nd, each podocyte bears foot processes associated with the investing b asal lamina; centrally, there is no conspicuous lumen. Such postcephal ic podocytes, either in compact glands or in a more diffuse arrangemen t, have also been found in decapods, mysids, and isopods, and perhaps occur in other crustaceans as well. Podocytes are known to filter hemo lymph and to pinocytotically extract constituents of the filtrate for modification and storage of residues. Histologically, the thoracic lim b glands of Hutchinsoniella are identical to the end sac of the maxill ary and antennal glands, but differ in not having a lumen or exit duct . The second maxilla lacks this gland, even though it is identical to thoracic limbs in every other way. On the basis of podocyte histology and distribution in the animal, we conclude that these glands are seri ally homologous to the end sac of the maxillary and antennal glands, a nd are descendant from the segmentally repetitious ancestral excretory system.