ITS INHABITANTS AND GUESTS. *" % 9 



those of the cells on the other side. This arrangement is called 

 " alternate." The different species of the genus Bugula, which 

 comprises the " bird's-head " zoophytes, are often found on the 

 Flustra. On the present specimen we observe a bunch of B. 

 aviadarta, Plate I., Fig. i (b). The Biigidce may be easily distin- 

 guished by the '^ avicularia " or bird's-head processes attached to 

 the sides of the zooecia. These are modified cells, taking in this 

 genus the form of birds' heads, with distinct beaks, which, during 

 life, are in constant motion fsee Plate L, Fig. 4). The object of 

 these curious structures is not properly made out. In some cases 

 they serve doubtless to catch passing prey, and hold it until 

 the polypide is ready to devour it, or until, by the decay 

 of some captured worm, crowds of infusoria are gathered 

 in the neighbourhood, but this cannot be the universal pur- 

 pose, as the appendage is fixed in some species so far from the 

 orifice as to be useless as a food-holder. One thing is clear that 

 they are modified forms of ordinary zooecia. The Rev. Thomas 

 Hincks has traced their development very fully from the zooecium 

 proper, through the various forms of fixed avicularia, to the free- 

 moving, jointed, and elaborate appendages of the Biigtdce. The 

 more common English species of the genus may be distinguished 

 from each other as follows : — B. pliwwsa has an elongated cell, 

 with a large orifice armed with a single spine ; B. turbitiata has an 

 oblong cell, with a single spine at each of the upper angles ; B. 

 avictdaria has two spines on the upper outer angle, and one on the 

 inner angle ; and B. flabellata has two spines (one much larger than 

 the other) on each of the upper angles. The modes of growth are 

 very varied. Plumosa grows in slender shoots ; Tiirbinata in grace- 

 ful spiral coils ; Avictdaria in small white tufts ; and Flabellata in 

 small but dense fan-shaped shoots, which are of a beautiful light 

 brown colour in life, but after death change to a dull ashy tint. 

 Amongst other species of Cheilostomatous polyzoa found on the 

 Flustra are the "Bull's Horn Coralline," Eucratea chelata (PI. II., 

 Fig. 10), which has the cells shaped like a "bull's horn" or a shoe, 

 and growing in single series ; the " Creeping Stony Coralline," 

 Scrupocellaria scrtiposa, which much resembles »S. reptans^ but has 

 only two spines, and wants the antler-shaped operculum ; and the 

 " Ciliated Coralline," Bicellaria ciliata, whose soft white feathery 



