A histological study of the food canal ofStrongylocentrotus franciscanus

Kurzfassung

Der Nahrungskanal des SeeigelsS. franciscanus besteht aus vier verschiedenen Abschnitten: Pharynx, Oesophagus, Darm und Rectum. Die Wandung des Nahrungskanals setzt sich zusammen aus einem äußeren Epithel, zirkulären und longitudinalen Muskelschichten, einer Bindegewebsschicht und einem inneren Epithel. In den Wandungen von Pharynx und Oesophagus gibt es zwei Arten von Sekretionszellen; eine liefert mucoide, die andere acide Sekretionsprodukte. Der Magen (erste Intestinalschlinge) ist mit einem inneren Epithel ausgekleidet, welches gelbliche Körner enthält, die extrazelluläre Enzyme produzieren. Im inneren Epithel von Darm (zweite Schlinge) und Rectum konnten keine Sekretionsgranula nachgewiesen werden. Lipoide und Glykogen scheinen in der hinteren Magenhälfte vorzukommen und in der vorderen Hälfte des Darmes. Die Aktivität der alkalinen Phosphatase ist beschränkt auf die freie Begrenzung des inneren Epithels von Magen, Darm und Rectum.

Summary

1. The wall of the food canal is composed of an outer epithelium, layers of circular and longitudinal muscles, a layer of connective tissue of varying thickness, and an inner epithelium generally composed of very tall, slender cells.

2. Two kinds of secretory cells are recognized in the pharyngeal and esophageal wall; one produces a mucoid secretion and the other an acid secretion. Numerous echinochrome containing amoebocytes and agranulocytes are distributed in the connective tissue layer and the basal region of the pharyngeal inner epithelium.

3. The stomach is lined with an inner epithelium containing yellowish granules, which are discharged from its surface to provide extracellular enzymes. Large eosinophilic granulocytes, which are assumed to participate in digestion by ingesting particles and absorbing dissolved nutrient substances, are sometimes found to be imbedded within the stomach inner epithelium. The intestine and rectum, however, have never been found to contain any secretory granules nor any amoebocytes in the inner epithelium. Echinochrome-containing amoebocytes, however, are found in all tissues of the food canal.

4. Lipids and glycogen appear to be deposited in the hinder half of the stomach and fore half of the intestine. Starvation for five weeks or more results in a significant decrease of these reserves.

5. Alkaline phosphatase activity is restricted to the free border of the inner epithelium of the stomach, intestine, and rectum.

6. It is concluded that the stomach functions in the digestion of foods, in absorption of the products of digestion, and that the intestine and rectum function as absorptive organs and a conductive tube for the elimination of undigested food materials.