328 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
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 hemal side; the peri- 
pharyngeal 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, mhz’, Mem. on Salpa) is a 
structure which I have found in all the ordinary Ascidians which I 
have examined. In Pyrosomea it is a sort of ridge or inward process 
of the inner tunic, less than ,35th of an inch broad, on 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 hemal 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 
cesophageal aperture, before reaching which the single ridge divides, 
and its branches soon cease to be further distinguishable. On the 
neural side, the two peripharyngeal ridges pass on to the elevation of 
the inner tunic in which the ciliated sac opens, and unite upon its 
posterior half, widening as they do so, whence their junction forms a 
triangular area with its apex directed backwards. 
The very singular structure which I formerly termed the exdos¢yle, 
and which I was at one time inclined to regard as a kind of internal 
shell, is, in reality, a longitudinal fold or diverticulum of the middle 
of the hamal wall of the pharynx, which projects as a vertical ridge 
into the hemal sinus, but remains in free communication with the 
pharynx by a cleft upon its neural side. In consequence of the 
thickness and opacity of the epithelium which lines the fundus of this 
