SUB-KINGDOM VI.— BRYOZOA 



[Or POLYZOA]. 



If OSS ANIMALS. 

 By R. Kiekpatkick. 



If the sea-weeda and shells cast up on the sea-shore be carefully examined, 

 some of these objects will probably be found overgrown by encrustations and 

 patches, which, viewed through a lens, resemble fine lacework or tracery of 

 varying pattern. Probably, also, some of the supposed sea-weeds themselves 

 will, on closer inspection, prove to be wholly different from plants, and to 



be, in fact, Bryozoa. Oae of the commonest of 

 these plant-like animals is the Sea Mat or Broad- 

 leaved Hornwrack {Mustra foUacea), (Fig. 1), 

 found all round the shores of Great Britain, 

 growing in shallow water, 

 attached to shells and rocks. 

 Ifc is often found in abun- 

 dance amongst the sea- 

 weeds cast up on shore, 

 especially after a gale. 



The Sea Mat forms thin 

 brown strap-shaped or fan- 

 shaped fronds, expanding 

 upwards from a flat, narrow 

 stem to a height of four to 

 six inches, and branching 

 in one plane. A very fine reticulate pattern is visible 

 on both surfaces. Under a low magnifying power this 

 appearance (Fig. 2) is seen to be due to the raised 

 margins of oblong boxes arranged in longitudinal rows ; 

 two spines rise from the margin on each side of the 

 rounded and expanded upper end, and frequently 

 a fifth spine between and above the lateral pairs. 

 The front of each box is covered with a roof of mem- 

 brane. On examining a fresh Itaflet in sea-water, 

 crowns of very slender tentacles will be seen to be 

 extruded through the upper ends of the front of the 

 boxes, a thin, horny, semi-circular lid being pushed up 

 during the process ; on the slightest alarm the ten- 

 tacles are rapidly withdrawn. It is also possible to see a bent tube beneath 

 the membranous roof. Each box or cell (Fig. 2) is the home of a polypide, 

 which has formed the cell. The tentacles of the polypide arise in a circle 

 from a platform, in the centre of which is an orifice, the mouth. 



665 



Fig. 1.— Flustra Foliacea. 



Fig. 2.— Flubtra (rnagni- 

 fifcd), showing- poljpiaes. 



a, Horoy lid. 



&, Avicularium. 



c, Egg capsule. 



