CRISTATELLA MUCEDO. 79 



different fi-om previous descriptions and figures, looked upon it as a new species, and named it 

 C. mirahilis* Adult specimens have since been found liy INI. Gervais, and I have met with 

 them in abundance in Ireland, and in other jDarts of the British Isles. 



A more interesting and beautiful animal than a fully developed specimen of Cristatella 

 mncedo can scarcely be imagined. The entire colony is of an oval shape, convex above and 

 flat below, where it attaches itself to neighbouring objects. Upon the convex surface are 

 arranged the orifices through which the polypides emerge, they are placed near the margin, 

 and run round the entire coencecium in three regular concentric series, which alternate with 

 one another, and leave an oval space in the centre where no orifices exist. 



In the middle of the flattened under surface is an oval disc, resembling the foot of a 

 gasteropodous mollusc ; on this disc, which is contractile, and admits of frequent change of 

 shape, the colony adheres to neighbouring objects, or creeps about on the submerged leaves 

 and stems of aquatic plants. From the edges of the disc a flat space extends outwards, 

 passing beyond the external series of orifices in the form of a projecting margin, whose interior 

 is occupied by a series of tubular cells or chambers, visible through the translucent skin, and 

 extending in a radiating direction from the disc outwards, but possessing no external opening. 



The tentacula are about eighty in number, being more numerous than in any other known 

 Polyzoon, except, perhaps, Pectinatella, Leidy. The coencecium is of a dull yellow, or sienna 

 colour. The polypide is nearly of the same colour, with the exception of the intestine, which, 

 in well-fed, healthy specimens, is light bluish-green. 



The largest specimens measure about two inches in length and a quarter of an inch in 

 breadth, and, with the polypides extended, are, at the first glance, not unlike certain hairy 

 caterpillars, or, as M. Gervais has aptly enough suggested, the silk fabric known by the 

 name of Chenille. Such large specimens are very sluggish, and change their place with 

 reluctance, at least when kept in confinement ; but specimens of about half an inch in length 

 creep about on the sides of the jar in which they are preserved at the rate of several inches in 

 the day ; they generally prefer keeping near the surface of the water, and seem to be much 

 under the influence of light; indeed, while the greater number of the fresh-water Polyzoa lurk 

 on the under surface of stones and in dark recesses, Cristatella loves to expose itself to the 

 full light and warmth of the sun. It differs, moreover, from all the Polyzoa with whose 

 habits I am acquainted, in the constant pleasure it takes in maintaining its polypides in the 

 exsei'ted state ; these, indeed, must be very roughly handled to cause them to withdraw into 

 their cells ; and the annoyance is no sooner removed than they again emerge. This exquisite 

 little Polyzoon seems, in fact, capable of existing only under the full influence of light, and in 

 the midst of the innumerable vortices excited in the surrounding water by the vibratile cilia of 



» 



its tentacles. 



The statoblasts are very characteristic. They are about ^K of an inch in diameter, 

 exclusive of the marginal spines, and, with the exception of the statoblasts of Pectinatella, 

 which they closely resemble, are larger than those of any other fresh-water Polyzoon. They 

 are also, with the same exception, the only ones having an orbicular shape. One face is a 

 little more convex than the other. The annulus is wide, very distinctly cellular, and of a 

 light yellow colour. The disc is deep reddish-brown, and elegantly mamillated. The spines 



* ' Report of Meeting of British Association, held at Ediuhiirgh, 1831.' 



