116 Dr Grant on the Structure and Nature ofFlustra. 



presents, in every stage of its growth, a regvilar form, and exact proportions 

 in all its parts ; it is composed of a continuous fleshy and calcareous substance, 

 like the outer part of the axis of the gorgonia, which the beautiful experi- 

 ments of Cavolini have shewn to be by far the most highly organised part of 

 that zoophyte, possessing distinct irritability, and secreting the horny layers 

 of the central part of the axis. The polypi are most intimately and inse- 

 parably connected with the axis by three parts of their body, and are only 

 digestive sacs or mouths developed by the axis, as in all other zoophytes, for 

 the nourishment of the general mass. By the axis of a zoophyte, I under- 

 stand every part of the body excepting the polypi, whether of a calcareous, 

 homy, or fleshy nature. The exact mathematical arrangement and forms of 

 the cells of Flustrce^ is incompatible with their existence, as separate and inde- 

 pendent beings, but is quite analogous to what we are accustomed to observe 

 in CellaricBy Sertularics, PlumularicB, and many other well known compound 

 animals. 



Although the ova of Flustrrc have been often observed, no one appears to have 

 hitherto examined either their mode of formation within the cells, or their nu)de 

 of developement after expulsion, so as to determine the real nature of these glo- 

 bular bodies, and the erroneous conjectures of naturalists respecting them 

 have greatly perplexed the history of this genus. The ova of the F. carbasea 

 make their first appearance as a small yellow point, a little below the aper- 

 ture of the cell, and behind the body of the polypus ; they are unconnected 

 with the polypus, and appear to be produced by the posterior wall of the cell, 

 in the same manner as the axis, or common connecting substance of the po- 

 lypi, produces them in other zoophytes. In this rudimentary state they are 

 found in the same cells with the healthy polypi, but, before they arrive at 

 maturity, the polypi of such cells perish and disappear, leaving the entire ca- 

 vity for the developement of the ovum. There are never more than one ovum 

 in a cell, and it occupies about a third of the cavity, when full grown and 

 ready to escape. When first visible it has a round or slightly oblong and re- 

 gular form ; when mature, it is ovate with the small end next the aperture 

 of the cell. The ova do not appear in all the cells at one time, nor is there 

 any discernible order as to the particular cells which produce ova, or the part 

 of the branch which contains them. Ceils containing ova are found alike on 

 every part of the branches, from the base to within two or three rows from 

 the apex, occupied only by young polypi. Sometimes we find half a dozen 

 or a dozen of contiguous cells all containing ova, sometimes two or three on- 

 ly ; and often such cells occur singly, at short and irregular distances from 

 each other. We find the ova, in all stages of maturity, on the same branch 

 at the same time ; and we seldom jbserve a specimen of the F. carbasea^ du- 

 ring the months of February, March and April, which does not contain nu- 

 merous ova. The ova have a lively yellow colour ; and when they occur 

 abundantly on a specimen or a part of a branch, they cause it to exhibit the 

 same lively hue, which is very different from the dull spotted brown appear- 

 ance which the branches present at other seasons. Cells are often observed 

 on different parts of the branches, containing neither polypi nor ova ; but the 

 fewness of these, and the great number of cells still containing only polypi at 

 the season of generation, render it probable that polypi are regenerated in the 

 empty cells after the escape of the ova. In the empty cells from which the 



