ANIMALS. 33 
calcareous matter in Hschara. It is this portion which constitutes aggregately the cells 
or polypidoms so beautifully preserved in the fossils, and remaining in the recent 
forms just named after the death of their tiny occupants. From my own observations 
on Flustra, Escharina, and some other allied genera, I am led to believe, that after the 
deposition of the base of the cell, the lateral perpendicular walls are first erected, and 
when they have been elevated to the proper height, the front wall is gradually formed, 
commencing with the lower or proximal part of the cell, and finishing with the 
aperture at the opposite or distal extremity. The entire substance of the cell is 
minutely porous; and in addition, the front wall is variously ornamented with large 
openings or foramina:’ it is also furnished, in certain genera, with some curious com- 
plicated structures (birds’ head and other processes), the economy of which is not at all 
understood. Reverting to the polyp; the upper portionof the sac, which is generally 
a soft, retractile, and transparent membrane, is crowned with, in many cases, a beautiful 
campanuliform appendage, consisting of rather long, delicate, tubular, ciliated tentacles, 
varying in number according to genera and species: in a species of Hscharina 
now under examination, there are about twenty-four tentacles. Within the tentacular 
cup is situated the mouth or oral aperture, which, according to the researches of 
Farre and other observers, leads into a long membranous gullet, at first considerably 
dilated and puckered, so as to resemble the branchial chamber of the Ascidians, and 
probably subserving respiration as well as deglutition (Milne Edwards). For some 
distance lower down, the gullet is contracted, ending in a gizzard of a rounded form, 
internally beset with minute teeth, and succeeded by a pouch-shaped stomach 
terminating at a short distance from the base of the cell. From the upper part of the 
stomach a narrow intestine ascends alongside of the gullet, terminating near the oral 
aperture, where it forms the cloacal outlet. The superior or soft portion of the sac 
can be withdrawn into the inferior solid portion or cell in the same manner as invert- 
ing the finger of a glove. When in this state, the polyp is protected by a corneous 
moveable lid or valvular fold of the integument fitting mto the aperture, and occa- 
sionally by a girdle of setz closely converging over the same opening. The gullet and 
intestine are folded somewhat in the form of a siphon. The protrusion and retraction 
of the soft portion of the polyp, and the various organs connected with it, are effected 
by means of muscles conveniently situated within the sac. When the polyp protrudes 
itself, the “ bundle of setze first rises out of the apex of the cell, and is followed by the 
rest of the flexible integument; the tentacula next pass up between the sete, and 
separate them ; the folds of the cesophagus and intestine are straightened, and when 
the act of protrusion is completed, the crown of tentacles expands, and their cilia 
commence vibrating.” 
1 The foramina are distinctly seen on the non-celluliferous surface of the Corals represented in Plate II, 
fig. 16; Pl. V, fig. 8. 
* Owen, Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, pp. 96-7. 
é 
