. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 52 POLYPIFERA. portion of the tegumentary membrane, which, by the molecular deposit of earthy matter in its tissue, becomes ossified, something like the cartilage of the higher animals, with- out ceasing to be the seat of nutritive move- ment. It is evident likewise that what is usually called the body of the Bryozoon constitutes, in fact, but a small portion of it, principally consisting of the digestive appa- ratus. As to the operculum, destined to close the entrance of the tegumentary cell, it is merely a lip-like fol
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 52 POLYPIFERA. portion of the tegumentary membrane, which, by the molecular deposit of earthy matter in its tissue, becomes ossified, something like the cartilage of the higher animals, with- out ceasing to be the seat of nutritive move- ment. It is evident likewise that what is usually called the body of the Bryozoon constitutes, in fact, but a small portion of it, principally consisting of the digestive appa- ratus. As to the operculum, destined to close the entrance of the tegumentary cell, it is merely a lip-like fold of the skin, the marginal portion of which acquires a dense consistency by in- terstitial deposit, while at the point where it is continuous with the general envelope it remains sufficiently soft and flexible to form a sort of hinge. The tegumentary sac, deprived of its car- bonate of lime, seems to be formed of a to- mentous membrane, covered, especially upon its inner side, with a multitude of cylindrical filaments, disposed perpendicularly to its sur- face, and closely crowded together. It is in the interstices left by these fibres that the calcareous matter appears to be deposited; for if a transverse section be examined with the microscope the external wall is seen not to be made up of superposed layers, but of cylinders and irregular prisms arranged per- pendicularly to the axis of the body. But the above are not the only arguments adduced by Milne Edwards in proof that these polyparies are maintained in vital connection with the animal. On examining the cells at different ages it is found that after they are completely calcified they undergo material changes of form. This examination is easily made, seeing that in many species the young sprout from the sides of those first formed, and do not separate from their parents ; each skeleton, therefore, presents a long series of generations linked to each other, and in each portion of the series the relative ages of the indi
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