36 ON POLYPS. 



oval membranous sac, but not in sufficient preservation to be 

 properly described. This was most probably the stomach. 



(49.) Around this sac, alternating with the tentacles, are eight 

 triangular filaments, (Jig. 9 ; 1 e,) which are at first free and 

 floating, but they soon become attached to a membrane which 

 lines the calcareous tube ; and, gradually diminishing in size, they 

 extend through its whole length. These filaments are analogous 

 to the ovaries of the Corallidse and Pennatulidse ; their inner sur- 

 face, in mature individuals, is studded with ova of different sizes 

 attached to them by short pedicles (Jig. 9 ; 8). 



(50.) At the point where the ovigerous filaments reach the ten- 

 tacles, a membrane is observable which assumes the shape of a 

 funnel when the animal retires into its shell, and at the open end 

 of the funnel the membrane is seen to fold outwards, and become 

 continuous with the calcareous tube; (Jig. 9 ; 1, &;) its inner sur- 

 face indeed is prolonged under the form of a thin pellicle over all 

 that part of the interior of the tube which is inhabited by the 

 polyp, terminating at a kind of diaphragm composed of the same 

 hard substance as the tube itself. The remains of these diaphragms 

 are found in the interior of old tubes at various distances from 

 each other. 



The funnel-shaped membrane does not terminate suddenly at its 

 point of junction with the calcareous tube ; the latter, indeed, is a 

 continuation and product of the first, the calcareous substance being 

 evidently deposited in this gelatinous membrane, in the same man- 

 ner as phosphate of lime is deposited in the bones of very young 

 subjects, changing its soft texture into hard, solid substance. The 

 manner, therefore, in which this tube is formed, cannot be compared 

 to the mode of formation of the shells of Serpulce or the shells of 

 mollusca; in the latter case it is a secretion from the skin, almost 

 an epidermic product, but in these polyparies there is a real change 

 of soft into solid substance, which is effected gradually, but not 

 deposited in layers. 



(51.) When the tube has acquired a certain height, the animal 

 forms the calcareous horizontal plate which unites it to those 

 around ; the still membranous upper part of the tube extends 

 itself horizontally outwards around the aperture, (Jig. 9 ; 2, 6,) 

 doubling itself so as to form a circular fold ; this part of the 

 membrane is no longer irritable ; its internal surfaces unite so as 

 not to interrupt the continuity of the tube ; carbonate of lime is 

 gradually deposited within it, and soon a prominent partition, com- 

 posed of two lamellae, soldered together through almost their entire 



