I2 Observations upon the Habits, Structure and [January, 
The odd tentacle which is found in the mouth circlet of 
Amphioxus, is formed from the center of the basal portion of 
cartilage from which the two rings originate. The cartilaginous 
portions of all these tentacles are curved inward, and so directed 
that the tentacles in the normal condition always cross each 
other, much as the fingers of a person’s hands can be interlaced, 
and thus form a rude sieve which prevents the entrance of large 
substances into the digestive tract. The pharyngeal ring which 
marks off the anterior limits of the abdominal cavity, forms a 
sort of welt or slight constriction around the inside of the ante- 
rior portion of the alimentary canal. It is curved backwards 
upon both sides, and bears upon the posterior border of each 
curved portion two or three rather large fleshy-looking tentacles. 
(Fig. 2, Pl. 1.) These tentacles generally lie directed backwards 
against the side walls of the digestive tract, but they can be brought 
forward so as to extend directly across the canal and form a sec- 
ond barrier to the onward progress of large bodies. In the young 
this barrier is of much greater service in preventing entrance to 
the digestive tract than the oral tentacles, as these latter appen- 
dages are not sufficiently numerous to act as an efficient guard 
until the animal is of considerable size, as large or larger than the — 
largest of my young specimens. These tentacles are not always l 
of the same size, and are generally so placed upon the sides that. 
when brought forward they alternate one above the other. 
The branchial arches are frame-like in structure, long and 
slender in outline, and run obliquely downwards and backwards 
across the entire width of the canal—this obliquity is such that 
the center of the upper portion of one arch is about over the — 
center of the lower part of the next arch in front. The arches 
are quite numerous, fifty, more or less, upon each side, but Iam _ 
not aware that there is any definite limit to their number, the _ 
largest individual appearing to have the most arches. The greater — 
number of them are of uniform length, but as they approach their 
posterior limits they gradually become shorter and shorter, to the 
last one or two, which are less than a quarter the length of the 
longest ones. The first and second arches are also much shorter 
than the others, and are about the length of the last ones. The ` 
first and last arches are very simple in formation. The first is : 
composed of an oblong framework, pointed at the lower end and 
nearly square or somewhat pointed at the upper. It is about 
