Dr Grant on the Structure and Nature ofFlustrte. S41 



undoubtedly produced by ciliae in that situation ; these minute 

 processes appear to be the only active organs in the circulation 

 of the fluids in zoophytes. The body of the polypus has the 

 usual red colour, while the head and arms are nearly colourless. 

 The long cylindrical and curved body of the polypus is tubular 

 to its posterior termination, which is shut ; and we can sometimes 

 perceive a small bolus of food moving to and fro in the conical 

 part of the body below the bifurcation. The globular sac in 

 this species does not appear to be connected with the formation of 

 the ovum, nor with the regeneration of new polypi in the old cells. 

 The ova of this species of flustra begin to appear early in au- 

 tumn, and continue to be generated in the cells during the whole 

 winter ; those of the F. carhasea make their appearance later in 

 the season ; and I have elsevyhere shewn, that, in other zoophytes, 

 different species of thesaine genus vary much in their season of 

 generation, thought/residing together on the same rock. The 

 ova first make tj:}eir appearance at the narrow base of the cells 

 as very small, pale- red, gelatinous spheres, and the polypi of 

 such cells ate generally removed, and only a small round dark 

 brown spot is seen in their stead, in the center of the cells. There 

 is but one ovum in each cell, as in other JlustrcB and calcare- 

 ous cellarice ; and, as it enlarges in size, it advances higher in 

 the cell, till, in its mature state, it occupies the broad upper part 

 of the cell. When the mature ovum is found at the summit of 

 the cell, we observe a distinct wide helmet-shaped capsule sur- 

 rounding it, and separating it from the cavity of the cell. By 

 examining the ovum within this capsule, with the microscope, 

 we perceive its cilise in rapid motion ; and I have frequently ob- 

 served the ovum, in this situation, contract itself in different di- 

 rections, shrink back in its capsule, and exhibit other signs of 

 irritability before its final escape. The helmet-shaped capsule 

 of the ovum is open at the top, and connected with the aperture 

 of the cell, so that the ovum readily escapes, by contracting its 

 body and moving its ciliae. On escaping from the cell, the ovum 

 glides to and fro by the action of its ciliae, and, after fixing, it 

 is converted into a single complete cell, from which new cells 

 shoot forward. Polypi make their appearance in shut sacs, at 

 the bottom of the new cells, when they are sufficiently formed to 

 protect them. When the ovum has escaped from the cell, the 

 dark round spot in the center of the cell enlarges, and a new po- 



