1880. | Development of Amphioxus Lanceolatus. 13 
twice as long as broad, almost upright in position, and is placed 
just posterior to the lower curvature of the pharyngeal ring. The 
last one is merely a round or nearly round ring of cartilage. The 
rest of the arches are shaped much like the first, but are bi-lobed 
above and have a central bar which passes from the indentation 
of the bi-lobed end down to the cartilaginous bed which encloses 
the pointed lower extremity. This bar is about twice as wide as 
either side of the arch, and is marked throughout its entire — 
length by a median line which indicates a division into two slen- 
der halves. In all of the longer arches there are also three cross- 
bars, which pass from side to side of the arch at about equal 
distances between the two ends, and in the shorter arches, except- 
the first and last, which contain none, there are sometimes one, 
sometimes two of these bars in each arch. These bars pass 
obliquely backwards and upwards across the arch, and generally 
go directly from one side to the other, but some of them divide 
at the central bar and become attached to it, so that they form 
two short bars instead of one long one. The arches of each side 
are placed close together, edge to edge, so that they have the 
appearance of a connected, continuous series of long slender 
oblique bars, each marked by a median division line and sepa- 
rated by a space of about the same width as the bars themselves, 
and with cross-bars running, with more or less regularity, across 
these spaces from alternate bars. The upper edge presents a — 
series of uniform lobes, and the lower edge a series of larger 
uniform arched points, there being left between each two points 
a triangular space of considerable size. (Fig. 4, Pl.1, æ.) Each 
complete arch is thus made up of two nearly similar halves, and - 
as the arches of the two sides alternate with each other, as has 
already been said, the triangular spaces at the bases of the arches- 
not only serve to show the divisions between them, but also indi- 
cate the positions of the opposite arches. This alternation can 
be readily seen by placing an adult animal, when living, under a _ 
low power of the microscope, or by a careful dissection of this 
portion of the body. 
The Digestive Tract—The alimentary canal, which witkad 
along beneath nearly the entire length of the notochord, is some- 
what compressed from side to side, varies considerably in breadth 
in different parts, and is lined throught its entire length with cilia __ 
which serve by their action to draw food into the canal for the — eS 
