204 PROFESSOR HUXLEY ON THE ANATOMY 
fact, three or four times as long as they are, and is divisible into a broad trilobed base, 
shaped somewhat like an ace of clubs, and a narrow fringe-like terminal portion. This 
may be distinguished by the title of the hcemal tentacle (PI. XXX. figs. 6, 6 a). 
The form, size, and relative position of the oral aperture remain the same in ascidio- 
zooids which have the oral aperture mounted upon a very short cone ; but as the cone 
enlarges, its haemal grows faster than its neural side, and finally becomes prolonged into 
the labial process, which bends over at a right angle to the direction of the axis of the 
zooid*. Concomitantly with, and apparently as a result of, this development of the labial 
process, the plane of the oral aperture gradually shifts, until, in the first place, it lies 
parallel with the axis of the zooid, and then continuing to turn, as it were, on its haemal 
margin, it eventually takes up a position perpendicular to the axis of the ascidiozooid 
again, but exactly the reverse of that which it had at first. The labial process so com- 
pletely overhangs the oral aperture when this stage is attained, that the free access of the 
water to the interior of the zooid must, one would think, be somewhat impeded. 
Two very delicate muscular bands, attached to the inner tunic, succeed one another at 
short intervals behind the aperture of the mouth, within which the buccal cavity rapidly 
widens, until it attains its maximum at about the end of the first fourth of the whole 
length of the zooid. At this point the buccal cavity ends and the pharyngeal or branchial 
sac commences, the boundary-line between the two being marked by the anterior end of 
the endostyle and of the epipharyngeal folds, in the middle line of the haamal side ; the 
peripharyngeal ridge at the sides, and the ciliated sac on the neural side. On each side, 
opposite the middle of the peripharyngeal ridge, is the circular patch-like yellowish organ 
regarded as the ovary by Savigny. 
The peripharyngeal ridge (ciliated band, mihi, Mem. on Salpa) is a structure which I 
have found in all the ordinary Ascidians which I have examined. In Pyrosoma it is a 
sort of ridge or inward process of the inner tunic, less than Tmnth of an inch broad, on 
9 00 
which the epithelial lining of the tunic is peculiarly modified, so as to present the 
appearance of a multitude of transverse rows of elongated corpuscles, each row being set 
obliquely to the long axis of the band, so as to be inclined from the ha3mal side and 
behind, forwards and to the neural side. These corpuscles are provided with short 
and delicate cilia. If the peripharyngeal ridge is traced upwards on the inner tunic, 
it is found to reach the anterior extremity of the cleft-like entrance to the endostyle, and 
there to pass into a narrow series of similar corpuscles which runs parallel with, and 
indeed may be said to form the outer part of, the projecting lip or epipharyngeal fold 
(' dorsal folds ' of Savigny and others) which bounds the entrance to the endostyle laterally- 
Arrived at the posterior extremity of the epipharyngeal fold, these prolongations of the 
peripharyngeal ridge, or, as they may be termed, epipharyngeal ridges, unite with one 
another and pass down as a single posterior epipharyngeal ridge along the middle line 
of the posterior wall of the pharynx to the oesophageal aperture, before reaching which 
the single ridge divides, and its branches soon cease to be further distinguishable. On 
In the figures given by Lesueur and by Savigny, the axis of the labial process is parallel with that of the body. 
In most of the ascidiozooids of my specimen, the end of the process is turned towards the hsemal side, but in some it 
is bent the other wav. 
