1880. | Development of Amphioxus Lanceolatus. 5 
aperture, the mouth, placed upon the median, ventral line just 
behind the depressed ram-like termination. of the body, and 
between it and the anterior portion of the abdominal cavity. This 
oral opening is of moderate size, and is surrounded by about 
thirty-one tentacles which are moderately long and slender, and 
bear upon their sides little protuberances which give them a | 
toothed appearance. The anus, or outlet of the canal, is funnel- 
shaped, and opens very eccentrically upon the left side of the 
body just beneath the level of the notochord and gwite near the 
end of the tail. The left or free edge of this aperture does not 
extend at its posterior limits quite down to the ventral edge of 
the muscle-plates, so that the anus also opens, to a certain extent, 
towards the left side of the body, although the foeces are expelled 
directly backwards and downwards along the side of the median 
fin. This free edge is quite flexible and in hardened specimens 
-is so contracted, together with the surrounding parts, that the 
anal aperture appears to open into a pseudo-cloaca. The integu- 
_ ment, which forms the greater part of the mouth tentacles, is thin 
and nearly transparent, and expands along the entire length of the 
dorsum, and around the tail, and as far forward as the branch- 
iopore, into a delicate, median fin of nearly uniform width except _ 
upon the edges near the posterior extremity, where two unequal 
lobes are formed which represent the blades of this “lance” ter- 
mination. Of these two “blades” the ventral is the larger, and 
its posterior curvature is nearly below the anal opening of the 
intestine. The integument also forms two longitudinal folds, - 
which extend along either side of the abdomen, from the poste- 
rior portion of the mouth orifice where they originate, to the 
indentation which exists between the abdominal and the tail 
portions. Here, after forming a sort of triangular pit into which 
the branchiopore opens, they become merged into the median, 
ventral fin, which, as already stated, reaches forward to this 
point. When the abdomen is fully extended these folds be- 
come nearly obliterated, and are barely visible as lines running 
along the sides parallel to and at some distance above the ven- 
tral outline; but when the abdomen is strongly contracted 
they form prominent ridges along the lower edge of the body, 
and so change the appearance of the specimen that it is not 
much to be wondered at that Pallas should say, that this por- : 
tion looked “very much like the very narrow foot of a Snail ce 
