4 Observations upon the Habits, Structure and | January, 
General Description and Habits—The adult Amphioxus, Fig. 1, 
Pl. 1, is a small, rather slender animal, which lives for the greater 
part of the time entirely buried in the sand along the sandy 
portions of the shores which it inhabits. When fully grown it is 
about two inches in extreme length, rarely somewhat longer, and 
of a pale flesh color which changes, when seen by reflected 
light, to a beautiful display of metallic iridescence. 
Its body is smooth, very muscular, much ‘compressed from side 
to side, and tapers gradually to the extremities, which are pointed, 
but differ considerably in contour, for while the posterior is lance- 
shaped, from whence is derived the specific name of /anceolatus, 
the anterior is formed like the ram of a modern gun-boat, and is 
admirably well adapted for forcing a way through the sand in 
which it burrows. The abdominal portion of this blade-like struc- 
ture forms a dilatable sack which extends from near the anterior 
end of the body back for about two-thirds the entire length of - 
the animal, where it terminates in an opening, the abdominal pore 
or branchiopore, which places the cavity enclosed by the sack in 
communication with the exterior. During the life of the animal 
this abdominal sack is seen dilating and contracting quite regu- 
larly, although at rather lengthy intervals, with « wave-like 
motion which begins at the forward end of the cavity and travels 
backward, rather slowly, to the posterior extremity. When the 
sack is completely distended this portion of the body presents a 
full, clear, rounded appearance, and projects considerably below 
the ordinary ventral outline, but when contracted, as it is in all 
preserved specimens, all appearances of a cavity disappear, leaving 
merely a slight indentation where the “ pore”’ is situated, between 
the abdominal and the tail portions. ae 
Through the center of the muscular part of the body, and - 
forming an axial support to the animal, there is a long, slender, 
semi-cartilaginous rod, which is pointed at each end, and which 
extends from the very point of one extremity to that of the other. 
This rod is composed of an external membraneous sheath enclos- 
ing a series of closely approximated flattened disk-like bodies, and | 
is probably the homologue of the vertebrate notochord, or back- 
bone, although not exhibiting any anterior cranial expansion. — 
_ Above it, but not extending quite as far forward, is the main nervous ~ 
_ system, or chorda dorsalis, and below it lies the long, nearly straight _ 
alimentary canal. This canal opens anteriorly by a longitudinal _ 
