The various views that have been put forward of the asymmetry of the amphioxus larva are discussed, and a modification of Garstang's view is proposed. Upon this view, the asymmetry of the amphioxus larva is directly related to its mode of feeding; the essentials of this process in the young larva are discussed and it is concluded that the body cilia play an important part in the feeding process. The derivation of amphioxus from the Ascidiacea is discussed, and various points are indicated which suggest that the original position of the mouth in the ancestry of amphioxus was ventral, as Garstang suggested.