Proteolytic digestion and the problem of the pancreas in the ammocoete larva ofLampetra planeri

Abstract

Remarkably little experimental work has been carried out upon the digestive system of the Cyclostomata. Alcock (1899) described the occurrence of peptic digestion in the ammocoete, but in view of the early date of this work and of the fact that the protease of the Tunicata is now known to be of the tryptic rather than the peptic type (Yonge, 1925; Berrill, 1929) the matter seems to demand reinvestigation. Moreover, recent histological studies on the “ pancreas ” and intestine of lampreys, to be described below, have led to conclusions regarding the distribution of the zymogen cells which have not yet been tested by experimental methods. The present work deals with these two problems, to the significance of which attention has already been drawn elsewhere (Barrington, 1935), and provides also a basis for a comparison of proteolytic digestion in the Cyclostomata with that in the Tunicata and in the Pisces. The ammocoete larvae ofLampetra planeriused in this work have been collected from the River Itchen in Hampshire at various times between April and September. Material for sectioning has been fixed in Bouin’s solution, Lane’s fixative, mercuric formol, and in Susa’s solution, and subsequently stained on the slide with Mallory’s stain, Heidenhain's haematoxylin, and by Lane’s method for zymogen granules. The experimental methods will be described later.