22 J. H. ORTON. 



and the atrium ; it is finally seen to pass out of the animal at the atriopore. 

 If now the pharynx of the living animal be examined carefully while 

 feeding is going on the process of collection of the food-particles may be 

 watched. As particles pass along the pharynx they may be seen to be 

 drawn up against the internal wall of this organ. Instead, however, of 

 becoming collected in the endostyle as has been generally stated to be the 

 case, the particles become caught in thin sheets of mucus and travel 

 dorsally on the internal wall of the pharynx towards the dorsal groove, into 

 which they disappear. If the animal is taking in a large number of food- 

 particles, thes-e often become worked up with mucus into a long cylindrical 

 mass which travels as a whole away from the endostyle towards the dorsal 

 groove, as is shown in Fig. 2. This figure is a drawing of a view of the 

 pharynx of a living animal seen through the transparent body wall, the 

 food-particles being visible through the gill-bars. Food-particles massed 

 together in various shapes may also be seen — like that depicted in the 

 middle of this figure just above the food-mass — all travelling towards 

 the dorsal groove, which in this way becomes very quickly charged with 

 the collected food. 



CILIAEY MECHANISMS ON THE GILL OF AMPHIOXUS. 



It is thus obvious that there exists some mechanism for collecting and 

 transporting food-particles along the internal face of the gill-bars. If a 

 portion of the living gill, such as that shown in Fig. 3, be now observed 

 in a little water in a watch-glass under the microscope, this mechanism 

 can be examined. The mechanism, however, is more easily made out if a 

 little finely powdered carmine be added to the water. Very soon after 

 the carmine grains are added they may be seen to be drawn towards the 

 internal face of the gill-bars, along which they are hurried in a direction 

 away from the endostyle, and may become collected into a cylindrical 

 mass such as is shown on the right side in Fig. 3. The arrows on this 

 side of the figure indicate the direction in which the particles and the 

 collected mass travel. Individual particles may be seen to travel at an 

 angle across the bars, i.e. in a ventro-dorsil direction, as is indicated also 

 by the arrows. The mechanism which causes the movement of these 

 particles across the gill-bars cannot be made out easily when examining 

 the gill from this point of view, but when a single gill-bar is examined in 

 side view, highly magnified (see Fig. 4), it is seen that on the internal face 

 of the bar there is a row of relatively short cilia (Fig. 4, fc.) which lash 

 rapidly along the length of the bar and thus effect the translation of such 

 particles as are drawn against it. That the particles are drawn against the 



