466 



POLYZOA 



so-called "sea-mat/' an old writer says: "For curiosity and 

 beauty, I have not, among all the plants or vegetables I have yet 

 observed, seen any one comparable to this seaweed." l Viewed 



with the microscope, the 

 frond is seen to consist 

 of two layers, placed back 

 to back, of oblong cham- 

 bers, each of which is the 

 dried body- wall of a single 

 individual. The whole is 

 obviously a colony, and 

 to this fact the term 

 Polyzoa refers. 



The chambers just 

 noticed are termed 

 " zooecia." Each is 

 rounded at one end, near 



Fig. 2S2.Flustra foliacea L., Cromer. A, Natu- which is the " orifice," 

 ral size, B' indicating the portion magnified in through which the teil- 

 B ( x 30) : a, avicnlarium with closed mouth, - , . . . . , 

 to the left of which are seen two avicularia with tacles 01 the living animal 

 open months ; o, ovicell, forming the upper can ^ p usne d Ollt. Two 

 part of a zooecium. Ovicells are seen on three in- 

 consecutive zooecia. The operculum, which short, Stiff spines usually 

 closes the orifice of the zooecium is seen in occur on each gide of th 

 different positions m the individuals figured. 



orifice ; and the symmetry 

 of this forest of spines fully justifies the above-quoted remark. 



The upper part of some of the zooecia is somewhat swollen, 

 these swellings representing the conspicuous " ovicells " of many 

 other genera. In the early part of the year each ovicell pro- 

 tects an orange -coloured egg or embryo, and the larvae are 

 readily liberated if the fresh colony be placed in clean sea-water. 

 " At least ten thousand " were hatched out in three hours from 

 a colony placed in a glass by Sir John Dalyell. 2 The larva 

 swims freely in the water for a short time, and should it find a 



Polyzoa in the Collection of the British Museum, Parts I. -III. 1852, 1854, 1875; 

 to the Challenger Reports on Polyzoa, Parts 30 (1884), 50 (1886), and 79 (1888) ; 

 for references and lists of species, to Vine's Report on Recent Marine Polyzoa, 

 Cheilostomata and Cyclostomata (Report, 55th meeting Brit. Ass. Aberdeen, 1885, 

 pp. 481-680) ; [and to Nickles and Bassler, Synopsis Amer. Foss. Bryozoa incl. Biblio- 

 graphy (Bull. U.S. Geol. Survey, No. 173, 1900)]. References to the literature of 

 the fresh-water forms will be found below, in Chap. XVIII. 



1 Hooker, quoted by Landsborough, Hist. Brit. Zoophytes, 1852, p. 346. 



2 Rare and Remarkable Animals of Scotland, ii. 1848. p. 15. 



