CHAPTER XVIII 



POLYZOA (continued} 



FRESH - WATER POLYZOA PHYLACTOLAEMATA OCCURRENCE - - 



STRUCTURE OF CRISTATELLA DIVISION OF COLONY MOVE- 

 MENTS OF COLONY RETRACTION AND PROTRUSION OF POLY- 



PIDES IN POLYZOA STATOBLASTS TABLE FOR DETERMINATION 



OF GENERA OF FRESH-WATER POLYZOA REPRODUCTIVE PRO- 

 CESSES OF POLYZOA DEVELOPMENT AFFINITIES META- 

 MORPHOSIS BUDDING. 



Fresh-water Polyzoa. Although the Gymnolaemata are 

 ordinarily marine animals, fresh-water examples from this Order are 

 not altogether wanting. The Ctenostomata among the typically 

 marine groups show the most tendency to stray into fresh-water. 



Alcyonidium and Bowerbankia (Fig. 238) flourish in estuaries, 

 while Victorella and Paludicella (Fig. 250) are only known as 

 fresh or brackish water forms. Victorella was named after the 

 Victoria Docks in London, where it was first found ; more recently 

 it has also been discovered in other parts of England and on the 

 Continent. 1 



The systematic position of the genera Hislopia and Norodonitt? 

 which have been described from fresh water of India and China 

 respectively, is at present uncertain. The undoubted Cheilostorm- 

 Miembranipora has, however, a British representative (3f. mono- 

 stachys), which occurs in brackish water, in ditches on the coast 

 of East Anglia. It is there known to form "friable, irregularly- 

 shaped, sponge-like masses," which grow on water-plants. 3 



1 Kraepclin, K., "Die deutschen Siisswasser-Bryoxoen." A bit. Vc,r. Ifambttrij, 

 x. 1887, No. 9, j). 95. 



- Jullien, Bull. Sue. Zwl. France, x. 1885, p. 92. 

 1 Hiucks, Brit. Marine Polijzoa, i. p. 1-32. 



