FLUSTRA, BUGULA, LEPRALIA. 



667 



i'ig. 4. — BnaDLA Tue- 



BINATA. 



the same level as the mouth opening. Further, all Bryozoa (excepting the 

 doubtful Phoronis) produce buds, which (excepting in Loxoaoma) remain con- 

 nected so as to form colonies. The colonies vary greatly in their composi- 

 tion, texture, and outward appearance. They may be etony, horny, and 

 flexible ; gelatinous, fleshy, or like leather or paper. They may form crusts 

 and patches, hard or flexible leaves, bushy or shrubby growths, stony 

 nodules, branches or plates, shapeless fleshy masses, etc. In all, we have as 

 the unit the polypide in its cell. Often the sime species occurs as a crust, or 

 in plates of single or double lamellte, the identity being revealed by the 

 characters of the individual cells composing the colony. A few typical and 

 interesting species will now be briefly referred to. * 



The Birds' Head Coralline (Bugula turhinata, Figs. 4, 5) forms 

 brownish horny tufts about two inches in height ; the branches, which are 

 arranged spirally round the stem, are very slender. The 

 cells are boat-shaped, and expand at the upper end. 

 The upper three-fourths of the front surface is mem- 

 branous, the rest of the cell being composed of hard, 

 horny material. At the upper part of 

 the membranous area is the lid, which 

 is pushed up when the tentacles are 

 extruded. The animal owes its popular 

 name to the remarkable avicularia 

 which arise from the edges of the cells ; 

 these organs consist of a short stalk, 

 a curved head and beak, and a horny mandible. The 

 " head " is filled with powerful muscles, which keep the 

 mandible continually snapping, the whole presenting a 

 ludicrous resemblance to a bird's beak (Fig. 5). 



In the Creeping Coralline {Scrwpocellaria reptans) a. 

 further modification of the cell is seen. At the back of 

 each ordinary cell is a very minute tubular cell known as a 

 vibraculum (bristle cell), with a cleft at the top in which 

 a long fine bristle is hinged. Sometimes the bristles are 

 all kept moving together like oars, or, again, individual 

 bristles may sweep round the front of the cells to clear 

 away debris or frighten trespassers. The cell and its 

 contained polypide are here reduced to a tubular cell 

 and muscular apparatus, while the lid of the ordmary cell 

 has become lengthened out and changed into a bristle. 



Brvozoa are perhaps most commonly met with m the form of crusts and 

 patches on stones, shells, and sea-weeds. The Lepralia of Pa.Uas(Lepralia 

 pallasiana (Figs. 6, 7) forms circular reddish-white 

 or vitreous patches on shells, etc. The cells are 

 arranged in radiating lines, each cell being a stony box 

 with a punctured pattern on the front surface. At 

 the outer end of the front surface is a square aperture, 

 surrounded by an elevated rim and closed by a horny 

 lid. One of the cells in the figure shows a lid partly 

 pushed up by the tentacles of the polypide in the 



interior. 



Fig. 6.-LBPRA11A Pal- All the species hithertoreferred to belongto theorder 

 LAsjANA (encruBting a chilostomata (lip-mouthed), which is characterised by 



Fig. 5.— Bugula 



(.magnified). 

 A, Avicularia. 



