192 



METAZOAN PHYLA 



The fresh-water bryozoans (Fig. 104) form moss-Hke colonies attached 

 to plants, sticks, or stones, usually near the surface of quiet water, 

 though they have been found in Swiss lakes at a depth of over 40 



Ovary, 

 S-f-omach 



; Lophophor-e 



Sf-cffob/asis 



Fig. 104. — Fresh-water bryozoans. A, colony of Plumatella sp., growing on a frag- 

 ment of a small branch of a tree. About natural size. B, several zooids of a colony of 

 Plumatella repens (Linnaeus), a European species. {From Allman, "Monograph of Fresh- 

 water Polyzoa.") Highly magnified. 



fathoms. Some have the power of movement, the whole colony very 

 slowly crawhng along on its base. These fresh-water forms have developed 

 a type of winter egg known as a statohlast (Fig. 105), which is produced in 



Fig. 105. Fig. 106. 



Fig. 105. — Statoblasts of two genera of fresh-water bryozoans. A, Plumatella. B, 

 Cristatella. Much magnified. 



Fig. 106. — Two specimens of Terebratella transversa (Sowerby), a brachiopod common 

 on the Pacific Coast. Natural size. 



the fall, inclosed in a chitinous shell, and may either fall to the bottom of 

 the body of water in which it is or float. Freezing does not interfere with 

 its development in the spring but rather seems to stimulate it. 



An enormous number of fossil forms have been described and some 

 of these are very similar to species now living. 



