aoe HOWARD AYERS 
Amphioxus: a) to keep the mouth, at times, wide open; b) to 
screen its entrance; c) to close it entirely; d) to serve on occasion 
as a strainer for the food current; e) to direct the food current 
to the-oral aperture. 
The major motions of the jaw apparatus are three. First, 
the motions of approximation and separation of the two arms 
of the loop, with the resultant interdigitation and separation of 
the tentacles. Second, the movement of elevation of the whole 
jaw apparatus to the roof of the oral hood so that its long axis 
lies nearly horizontal and parallel to the notochord, this move- 
ment affecting the posterior end of the loop most, and that of 
the depression of the jaw apparatus resulting in the increase of 
the vertical diameter of the buccal cavity. Third, the retrac- 
tion and extension of the jaw apparatus due to the pull of muscles 
attached to the base of the loop and to the general contraction 
of the walls of the oral hood and body wall. The buccal frame- 
work can thus be withdrawn entirely within the oral hood or 
fully protruded as a projecting structure beyond the limits of 
the oral aperture. | 
The jaw apparatus arises in the young Amphioxus in the lip 
fold as two skeletal bars symmetrically placed on either side 
of the sagittal plane. These bars begin at the middle of the 
lower lip fold and grow outwards, then upwards, and forwards 
into and through the edge of the lip fold. The bars send out 
buds at intervals which later form the tentacles. These buds 
of the jaw bars push the muscular layer, the connective-tissue 
layers and the covering epithelium before them in such a manner 
that they fit over the skeletal axis of each tentacle as the finger 
of a glove covers a finger, except that the muscles extend only 
part way up the tentacle. 
Amphioxus—jaw nerves 
The researches of Hatschek, Heymans and van der Stricht, 
van Wijhi, Kutschin, Dogiel, and others, as well as my own, 
on the nerves of the head of Amphioxus have one outstanding 
result, viz., the oral hood is under the control of five pairs of 
