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. 232. Flustra foliacea L., Cromer. A, Natu- which is the " orifice," 



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



B ( x 30) : a, aviculavium with closed mouth, .,... i 



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



open mouths ; o, ovicell, forming the upper can b e pushed Ollt. Two 

 part of a zooecium. Ovicells are seen on three * 



consecutive zooecia. The operculum, which Short, Still Spines usually 



closes the orifice of the zooecium is seen in ^^ Qn each gide Q f the 

 dinerent positions in 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) ; and 

 particularly to Vine's Report on Recent Marine Polyzoa ; Cheilostomata and Cyclo- 

 stomata (Report, 55th meeting Brit. Ass. Aberdeen, 1885, pp. 481-680). This 

 Report contains lists of species from various localities, as well as references to the 

 works of previous writers, and much other valuable information. 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. 846. 



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



