14 Observations upon the Habits, Structure and (January, — 
nourishment of the animal. The canal may be divided into five 
rather natural divisions; the mouth cavity, extending from the 
mouth orifice to the pharyngeal ring; the pharynx, the cesoph- — 
agus and the stomach, extending from the pharyngeal ring to — 
the division between the abdomen and tail, and which hang from — 
their attachment beneath the notochord freely suspended in the | 
abdominal cavity, being completely enclosed by its walls; and : 
the intestine, which extends along through the tail portion of the — 
animal to the anus, near the posterior extremity. The mouth — 
cavity, or first division of the canal, is somewhat triangular in i 
shape, being circumscribed above by the notochord, and below 
and behind by the two orifices already mentioned. Its anterior — 
upper outline is curved, and it bears upon its walls certain slight, 
finger-like ridges where the cilia of this cavity are principally 
aggregated. 
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SES PARAE AEE AOI a RRL E S SAIN MENSAE A ERPS PT N Cele N APE eae a ST PEREA RET PEND an Meee ee 
At the rather constridted opening of the pharyngeal ring it 
merges into the pharynx, which extends a little past the middle 
of the abdominal cavity, and is the largest division of the canal. 
This portion is that in which the branchial arches are formed, and 
has much the shape of a bean pod, being quite broad along the — 
central part and narrower towards each end, but the posterior — 
extremity tapers much more gradually than the anterior, and where — 
it merges into the cesophagus, it is hardly more than half the size 
of the portion at the pharyngeal ring. Along its sides, in all the — 
spaces between the bars of the branchial arches, there are long 
narrow openings, called branchial slits, which place the interior 
of the pharynx in communication with the abdominal cavity, 
which is also known as the branchial cavity, or atrium, but which | 
might more properly, perhaps, as will be noted later on, be = 
called the dranchium. These branchial slits extend, with few ex- 
ceptions, from the upper curves down through nearly the entire 
length of the arches, to the edges of the cartilaginous, trough- 
like bed, being crossed here and there by the cross-bars which _ 
serve to stiffen the general framework. In the first two or three 
arches the clefts do not extend quite to the upper borders. Along 
the inner edges of these slits the cilia of the pharynx are very 
long and arranged in rows completely encircling each slit (Fig. Ay 
Pl. 1), so that by their action they intercept the food particles 
