Bilateral Asymmetry Shown by the Metachronal Waves in Protochordate Gill Slits

Abstract

MULLER¹ stated that metachronal waves travelled round the gill slits of Amphioxus "am vordern Rande aufwarts, am hinten abwarts" ; but he figured them moving in the opposite direction on the left side of the pharynx. Franz² did not clear up the contradiction, though he, too, noted and figured the metachronal waves. Fedele³, in a figure of the gonozoid of Doliolum mulleri, indicated by arrows the movement of the metachronal waves around the stigmata. The movement appeared anti-clockwise on both sides, seen from outside the pharynx. McGinitie⁴, examining the pharynx of Ascidia californica through the transparent test, also noted that the motion was anti-clockwise. Since he did not state from which side of the animal this observation was made, it might be inferred that the direction appeared the same from both sides ; but McGinitie did not specifically affirm this nor did he direct attention to the functional asymmetry implied. If the animal were bilaterally symmetrical in this respect, the movement would appear anticlockwise from one side but clockwise from the other, like the wheels of a car in motion.