232 THE MICROSCOPE. 



the polyp, and appear to be produced by the posterior wall of the 

 cell, in the same manner as the axis, or common connecting sub- 

 stance of polyps, produced them in other zoophytes. In this rudimen- 

 tary state they are found in the same cells with the healthy polyps ; 

 but, before they arrive at maturity, the polyps of such cells perish and 

 disappear, leaving the entire cavity for the development of the ovum. 

 There is 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 regular 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. Cells containing ova are 

 found alike on every part of the branches, from the base to within two 

 or three rows of the apex occupied only by young polyps. 



Dr. Grant, in writing more especially of the F. carbasea, says : 

 " They are very irritable, and are frequently observed to contract the 

 circular margin of their broad extremity, and to stop suddenly in their 

 course when swimming ; they swim with a gentle gliding motion, 

 often appear stationary, revolving rapidly round their long axis, with 

 their broad end uppermost, and they bound straight forward, or in 

 circles, without any other apparent object than to keep themselves 

 afloat till they find themselves in a favourable situation for fixing and 

 assuming the perfect state. The transformation of the ova, from 

 that moving, irritable, free condition of animalcules, to that of the 

 fixed and almost inert zoophytes, exhibits a new metamorphosis in 

 the animal kingdom not less remarkable than that of many reptiles 

 from their first aquatic condition, or that of insects from their larva 

 state." 



Flustra amcularis. This is another of the little beauties of the 

 deep, found usually on old shells, an inch in height, spreading itself fan- 

 like, and of an ashy colour, deeply divided in a dichotomous manner 

 into narrow, thin, plane segments ; truncate at the end, formed of four 

 or five series of oblong cells, capped with a hollow, globose, pearly oper- 

 culum seated between the spines, of which there is one on either side 

 of the circular aperture. The opercula are so numerous that they give 

 to the upper surface the appearance of being thickly strewn with orient 

 pearls ; the under surface is even and longitudinally striated, the num- 

 ber of stria3 corresponding to the number of rows in which the cells 

 are disposed. Dr. Johnston describes, amongst many other British 

 species, F. membranacea, "a gauze-like incrustation on the frond of 



