ANIMALS. 33 



calcareous matter in Eschara. 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 Escharina 

 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 can be withdrawn into the inferior solid portion or cell in the same manner as invert- 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 into the aperture, and occa- 

 sionally by a girdle of setse 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 setae 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 setse, and 

 separate them ; the folds of the oesophagus 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; PI. V, fig. 8. 



^ Owen, Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, pp. 96-7. 



e 



