102 VIGNETTES FJWM IXVIfSIBLE LIFE. 



altogether part company with the colonial struc- 

 ture. This compound structure is named the 

 Ctenacivm, and is spoken of as " an assemblage of 

 little cells " or chambers, in which the several 

 members of the colony or polypides are lodged. 

 It is, however, as we have described it, part and 

 parcel of the polypides themselves, each little cell 

 or chamber being an individual polypide, though 

 united to a common whole by their investing mem- 

 branes. These colonial structures of living animals 

 are found generally attached by a viscid secretion to 

 aquatic plants : some prefer the under- side of the 

 broad leaves of the water-lily, where they spread 

 themselves in an irregular kind of network against 

 the leaf ; others twine around the stem or on bits 

 of stick or rotten wood, sometimes in large irregular 

 masses or in spindle-shaped forms of considerable size; 

 others are found twined in long branching colonies 

 along with the coarse filamentous algae at bottom 

 of deep ponds or canals. I have found one of the 

 most beautiful and largest forms i.e., Lopltopus 

 crystaUinus hanging like bright beautiful blossoms 

 on the too common Anacharis, in the clear water of a 

 shallow pond a beautiful picture even to the naked 



