SERTULARID^E. 205 



spherical, composed of minute transparent granules, ciliated on the 

 surface, and distinctly irritable. There are only two ova in each 

 vesicle ; so that they do not require any external capsules, like those of 

 the Campanularia, to allow them sufficient space to come to maturity. 

 On placing an entire vesicle, with its two ova, under the microscope, 

 we perceive through the transparent sides the cilia vibrating on the 

 surface of the contained ova, and the currents produced in the fluid 

 within by their motion. When we open the vesicles with two needles, 

 in a drop of sea- water, the ova glide to and fro through the water, at 

 first slowly, but afterwards more quickly, and their cilia propel them 

 with the same part always forward. They are highly irritable, and 

 frequently contract their bodies so as to exhibit those singular changes 

 of form spoken off by Cavolini. These contractions are particularly 

 observed when they come in contact with a hair, a filament of conferva, 

 a grain of sand, or any minute object ; and they are likewise frequent 

 and remarkable at the time when the ovum is busied in attaching its 

 body permanently to the surface of the glass. After they have fixed, 

 they become flat and circular, and the more opaque parts of the ova 

 assume a radiated appearance ; so that they now appear, even to the 

 naked eye, like so many minute grey-coloured stars, having the inter- 

 stices between the rays filled with a colourless transparent matter, 

 which seems to harden into horn. The grey matter swells in the centre, 

 where the rays meet, and rises perpendicularly upwards surrounded by 

 the transparent horny matter, so as to form the trunk of the future 

 zoophyte. The rays first formed are obviously the fleshy central sub- 

 stance of the roots ; and the portion, of that substance which grows 

 perpendicularly upwards,, forms the fleshy central part of the stem. As 

 early as I could observe the stem, it was open at the top > and when it 

 bifurcated to form two branches, both were open at their extremities ; 

 but the fleshy central matter had nowhere developed itself as yet into 

 the form of a polyp. Polyps, therefore, are not the first formed of 

 this zoophyte, but appear long after the formation of the root and stem, 

 as the leaves and flowers of a plant." 



Attached to fuci and sea-side shells in abundance on the southern 

 coast of England, is found Plumularia cristata* It is affixed by a 

 horny, branching, interlacing, tubular fibre to the object on which it 

 grows. At different parts there are plumous shoots, usually about a 

 little more than an inch in height. The cells are of a yellow colour, 

 set in the stalk, of a bell-shape, and are compared to the flower of the 

 lily of the valley; the rim is cut into eight equal teeth; the polyp 

 minute, delicate; tentacles ten, annulated; mouth infundibuliform. 



