FRESH-WATER POLYZOA. 247 



ported elsewhere, and therefore seems to be exceed- 

 ingly rare in this country. In Europe it was the first 

 member of the Polyzoa to be discovered, as it was by 

 Trembley, the famous experimenter with Hydra, one 

 hundred and fifty years ago. The only known species 

 has been named Lophopus Trembleyi in his honor. 



The colonies form small jelly-masses attached to the 

 rootlets of Lemna, to floating sticks or to other sub- 

 merged objects, these little masses being slightly 

 motile, after the manner of Cristatella, as affirmed by 

 some observers and denied by others. The masses are 

 transparent, the attached base in the old colonies be- 

 coming opaque while in the young it is as hyaline as 

 the rest of the mass. The jelly-masses are at first sac- 

 like, finally becoming lobed or even branched. The 

 polyzoa are irregularly scattered throughout the colony, 

 extruding the horseshoe-shaped lophophore as do 

 the other and commoner forms. 



Lophopus as a colony varies from one-tenth to one- 

 half inch in diameter, each mature member of the 

 cluster bearing from fifty to sixty tentacles on its 

 lophophore. The statoblasts are produced in two 

 forms, both of which are shown in Fig. 175. 



4. Plumatella (Fig. 170). 



The tubes containing the animals may be attached 

 only at the base, or the whole colony may be adherent 

 to the submerged surface on which it grows. It is to 

 be found in shallow water, usually near the shore. 



To see the lophophore and expanded tentacles, if 

 the colony is small, it may be removed by slicing the 

 wood to which it is attached, the slice to be placed in 

 a watch-glass of water on the microscope stage, which 



