HISTOLOGICAL STUDIES ON THE DIGESTIVE SYSTEM OF A STARFISH, HENRICIA, WITH NOTES ON TIEDEMANN'S POUCHES IN STARFISHES

Abstract

In the digestive system of Henricia, regional specialization involving particularly the lining epithelium has segregated areas of zymogenic and mucous secretion from other areas adapted for current-production. Secretory areas include 5 interradial pouches and vesicles of the cardiac stomach, pyloric stomach (especially its radial reservoirs), and the median ducts and lateral diverticula of the pyloric caeca. Current-producing areas include 5 radial pouches of the cardiac stomach, gutters leading upward to marginal openings low in the pyloric stomach, and especially the very elaborate Tiede-mann''s pouches arising in pairs from these openings and extending along the oral midlines of the caeca. Starfishes such as Asterias lacking Tiedemann''s pouches, largely restrict their zymogen cells to the lateral diverticula of the caeca and crowd current-producing and mucous cells into the median caecal ducts, an area which in Henricia contains an extremely rich concentration of zymogen cells. Tiedemann''s pouches in Henricia are divided into many parallel flagellated channels leading diagonally upward into the pyloric caeca. The channels are separated by unique partitions formed by adhesionr seams between opposite side-walls of the pouch. It is evident from their structure and anatomical relationships, and has been experimentally demonstrated, that Tiedemann''s pouches are flagellary pumping organs of great effectiveness. The currents they produce are capable of drawing suspensions or solutions from the stomach and delivering them rapidly along almost the entire length of the pyloric caeca. Centripetal currents stream back into the stomach aborally, and thus a constant circulation of materials can be maintained through the radial secretory and absorptive areas, depending chiefly upon currents generated in the close-set channels of the 10 Tiedemann''s pouches. The customary food and the feeding habits of Henricia are unknown, but several lines of evidence, anatomical and experimental, combine to suggest that this starfish, like at least 1 other (Porania), may subsist either wholly or in part upon suspended matter gathered by a flagellary-mucous mechanism. Patiria miniata has well-developed Tiedemann''s pouches superficially resembling those of Henricia but fundamentally dissimilar, lacking the adhesion-seams that separate the flagellated channels in Henricia. Although they function similarly, these simpler pouches are probably less effective in current-production. Asterina gibbosa has Patiria-type Tiedemann''s pouches; Astropecten. in which the pouches were originally described (1816), has relatively small ones of simple construction. Both Patiria and Astropecten have been suspected of supplementing their macrophagous diet by particle -feeding, and their pouches are probably of significance in this connection. Linckia, not at all closely related to Henricia, has Tiedemann''s pouches and other specializations of the digestive system similar in many respects to those of Henricia. It is suggested that in all forms where they are present, Tiedemann''s pouches represent solutions to the problem of increasing circulatory efficiency within the digestive tract. Detailed studies on many species of starfishes now known only from external anatomy and skeletal features of preserved specimens will provide information upon which to base broader and more meaningful comparative surveys of internal specializations.