WORMS, ROTIFERS, LEECHES, POLYZOA 89 



the young are hatched they remain within the cocoon for some 

 twenty or thirty days before making their escape. They do not 

 undergo a metamorphosis, and although in some species the sexes 

 are separate, they are united as a rule. Of the marine leeches the 

 Skate-sucker (Pontobdella muricatd) is of interest as being the 

 transmitting agent of a Trypanosome (T. Raii) from one ray to 

 another. 



There are a number of marine worms which, from their bolster- 

 shaped bodies, resemble at first sight some of the Holothuria, or 

 Sea-cucumbers, belonging to the Echinodermata Their bodies 

 are usually long and cylindrical, destitute of parapodia or false- 

 feet, and unsegmented. These animals comprise the Qephyrea, 1 

 and were so named by Quatrefages, who considered them as form- 

 ing a bridge between the Worms and the Echinoderms. All are 

 marine, and while some live in the shells of molluscs, others fre- 

 quent the interstices between corals, or the sand and mud at the 

 bottom of the sea. The sexes are separate, and the young undergo 

 a metamorphosis. 



The Polyzoa are a most interesting group of animals, chiefly 

 dwellers in the sea, and, with one exception, form more or less 

 extensive colonies. The most familar are the Sea-mats (Flustra), 

 whose pale brownish, almost leaf-like colonies are to be found on 

 every shore. They are known by several popular names, such 

 as " Sea-mats," " Horn-wracks," " Moss-animals," and " Lace- 

 corals," all terms more or less descriptive of their appearance ; 

 while to science they are known by two names, Polyzoa and 

 Bryozoa, the latter being chiefly used by Continental writers. 

 Polyzoa was the name given to these animals by the English 

 naturalist J. V. Thompson, and has undoubted priority over 

 the term Bryozoa assigned to them by C. G. Ehrenberg in 

 Germany. 2 



Often very plant-like in their growth, it is not surprising to 

 find that the Polyzoa were at first mistaken for seaweed, and later 

 placed under the head of " Zoophytes " or plant-animals, before 

 their real character was discovered. If we examine the leaf-like 

 expansion of the Common Sea-mat (Flustra foliacea), we shall see 



1 Greek gephtira, a bridge. 



2 For a concise account of the controversy over these two names, see Hincks's 

 " History of the British Marine Polyzoa." 



