1880. ] Development of Amphioxus lanceolatus. 85 
left side of the anterior end, a short distance back from the 
extreme point of the body. The middle part of the tubular por- 
tion of the central cavity now enlarges into a small oblong 
stomach, with obliquely-placed cilia along its walls, and openings, 
formed by ingrowths of cells from the exoderm, appear upon the 
left side of the body, one at either end, placing the central cavity 
in communication with the exterior. The posterior of these 
openings is formed at the very extremity of the cavity, at the 
base of the exodermic tail expansion, and at or near the point of 
closure of the blastopore, and it may be that it is rather a reopen- 
ing of the old gastrula mouth than a new formation, although 
the latter seems to be the opinion at present. It is small, slightly 
dilatable, and becomes the anal aperture of the intestine. The 
anterior opening penetrates the body wall along the anterior half 
of the pharyngeal portion of the cavity and becomes the mouth 
orifice. It is at first a short longitudinal slit, but soon broadens 
into an oval aperture of considerable size, with long, slender, 
alternating, teeth-like processes extending out from the edges 
towards the center as guards to the entrance, and a thickening of 
the body wall takes place just below it, forming a prominent 
ridge-like border extending from near the median line below the 
cartilaginous, pear-shaped welt, backwards and upwards to very 
nearly the level of the notochord. Along the inner, lower edge 
of this mouth-ridge there are generally two or three slender 
pointed processes which lie close to the body and point towards 
the right side. The central cavity is thus at once transformed _ 
into a digestive tract, the food particles being drawn in at the 
mouth by the action of the internal cilia, passed on to the 
Stomach, where they are twisted and ground up for the nutrition 
of the animal, and the refuse material sent onward to the anus — 
and so out of the body. . ae 
A third opening now makes its appearance, piercing the body : ss 
Wall upon the median ventral line just below the mouth orifice. 
It is somewhat larger than the anal opening, longer than broad, _ 
| with the longer diameter transverse to the length of the body, te 
Pa which open along the under side of the pharynx at regular a 
| stances back to very near the middle of the body. Coincident 
With the formation of this first pharyngeal cleft, two 
ee. F í 
- Early stages in the development of Vertebrates. F. . Balfour. 
n Mic, Science, Vol. xv, p. 208. Camb., 1875. 
and forms the first of a series of ten or eleven similar pharyngeal 
