292 TOILERS IN THE SEA. 



small, but the colonies, or aggregations of individuals, 

 are often of considerable size. All of them appear 

 to be gregarious, flourishing in companies, and the 

 number of species must be very large, for they 

 have a wide, and almost unlimited, distribution. 

 Along our own shores it would be difficult to 

 say where we should find no trace of them. Some 

 of the encrusting species are found flourishing 

 on almost every dead shell, and often whilst the 

 mollusk is still living ; others flourish on stones and 

 rocks which are submerged, and a large number 

 attach themselves to sea-weeds. They will be found 

 encrusting wood, stones, crabs, lobsters, or attached 

 to zoophytes, or even other species of Polyzoa, and 

 indeed seem to be almost ubiquitous in the sea. Their 

 general structure it must be our first endeavour to 

 attempt to elucidate. 



There is a superficial resemblance in some of the 

 species to the common Hydroid zoophytes, but, ex- 

 amined more closely, the animal will be found to be of 

 the molluscan type, and not that of the Hydroids. 



Elsewhere we have given a summary of the general 

 type of Polyzoon, 1 after Professor Allman, to the 

 following effect : " Let us imagine an alimentary 

 canal, consisting of oesophagus, stomach and intestine, 



1 "Natural History Rambles : Ponds and Ditches," p. 132, 

 1880. 



