84 ZOOPHYTES. 



Thus, whatever I shall continue to say, must be regarded as mere 

 notes, liable to revisal and correction. At the same time, these remarks 

 are not intended as impugning the unity of design. 



The Membranipora pilosa is one of the more diminutive zoophytes, 

 which should be perhaps deemed an investing calcareous, more than a 

 membranaceous incrustation. In general, if not always, it is a parasite. 



Its genuine colour is white, but it often partakes of the hue of the 

 substance invested. 



I cannot affirm what may be the most luxuriant state of this product. 

 But, in earlier, and I apprehend also in later stages, it is composed en- 

 tirely of a stratum of irregularly elliptical, dentate, superficial cells. A 

 profusion of very long, slender, rigid bristles, covers the surface of the 

 stratum. 



If the stratum thicken with age, the colour of the substance in- 

 vested may then have little effect on its appearance. It follows the form 

 of the substances invested ; which seem in preference to be the slender 

 Algae or Sertulariae. Thus, specimens of the Sertularia falcata bear it in 

 great abundance. 



The elliptical orifice of the cells, studding the crust, wherein sunk, 

 is guarded by eight marginal spines, about as long as equal to half the 

 width of the cell. They are white, and incline slightly over the cavity. 

 The long bristly processes, besides, are dispersed over the whole product. 

 Dr Fleming remarks, in his distinct and accurate description, that " the 

 spine or tooth, near the base, is prolonged into a long bristly hair." 



I feel much disposed to conclude that there are either varieties of the 

 Membranipora pilosa, or that some are totally divested of the bristles, 

 which, indeed, seem little calculated for resistance. 



A specimen, investing one of the delicate Alga 1 , is represented 

 Plate XVIII. fig. 16 ; and a portion as viewed by the microscope, fig. 17. 



The cell is inhabited by a very vivacious, light grey, ascidian hydra, 

 with 12 tentacula ; at least, these have been ascertained, in some individuals, 

 fig. 18. As the one cell lies partly under another, the animal issues 

 upwards, from below, to display itself. 



There may be specimens, whether identical or kindred, wherein the 



