8 A PIECE OF HORNWRACK : 



marine Polyzoa are divided into two groups, the Ectoprocta, 

 in which the orifice leading from the intestine is outside the tenta- 

 cular bell, and the Endoprocta, in which both the orifices of the 

 alimentary canal are within the bell. About the latter of these 

 groups I do not propose to say anything. The Ectoprocta are 

 divided into three suborders, the Cheilostomata, Cyclosto- 

 MATA, and Ctenostomata. In the first of these — to which the 

 Flustra itself belongs — the orifice of the cell is protected by a 

 moveable operculum or valve. In the second suborder the cells 

 are tubular, and the orifice has no such moveable operculum, al- 

 though Mr. Waters (Trans. Lin. Soc, Vol. XVII. , Zool.^ page 400) 

 has pointed out that in all this group there is a calcareous partition 

 which closes up the cells, in order probably to protect the tubes of 

 the colony from being choked up with mud and dirt, on the death 

 of the terminal polypides. To this suborder belong the Crisice^ 

 which I shall shortly describe. In the third suborder the poly- 

 pides never form calcareous cells, and the cell-orifices are pro- 

 tected, not by opercula, but by fringes of seice or bristles. 

 An example of this class will be referred to later. 



Such an expanse as that formed by the frond of the Flustra 



is a convenient locality for the founding of other colonies of 



Polyzoa, and accordingly we find several species growing here 



and there upon its segments in great luxuriance. First, we 



notice the " Creeping Coralline " or Scrupocellaria reptans^ 



Plate I., Fig. i (a)^ a species that rejoices in at least a dozen 



synonyms. In the catalogue of slides of a leading Microscopical 



Society this species occurs under three different names. Heptans, 



or creeping, has always been the favourite specific appellation, 



and is a very suitable one. The zoophyte creeps along the 



surface of stones, algae and other zoophytes, and forms crowded 



patches. Under the microscope each cell is seen to be armed with 



four spines, and protected by an operculum, which has a distinct 



antler shape (Plate L, Fig. 3). When once this operculum is seen, 



no mistake can be made as to the species under consideration. 



Each cell is also armed with a long whip, called a vihraciduin^ 



which sweeps the cell clean, and no doubt wards off intruders. 



The cells are oval, and arranged in a double line side by side, but 



so that the orifices of the cells on one side are half way between 



