82 POND LIFE 



About August spermatozoa appear, and fertilise the ovules in 

 that same individual, for Polyzoa are hermaphrodites (both male 

 and female in one). The next method is by the production of 

 statoblasts, formerly thought to be winter eggs, but to-day 

 considered to be buds. These structures are formed inside the 

 creature by a particular part known as the Funiculus. Each 

 statoblast is surrounded by a layer of aircells, so as to make it 

 lighter, and thus able to float more easily. The shapes are 

 various ; some are round, others egg-shaped, and yet others are 

 adorned with hook-like projections. In fact each species has 

 its typical statoblast. After resting for a certain time the 

 statoblast germinates, and on the case splitting a young colony, 

 containing at least ono fully grown member, makes its appear- 

 ance. The number of statoblasts produced by a single indi- 

 vidual is probably very great indeed. Under the microscope 

 it is often quite easy to count thirty or so of these structures, 

 in various stages of development. Certain species are able to 

 form winter buds known as " hibernacula." 



On the approach of cold weather the parent colony loses its 

 vitality, and produces these winter buds. Subsequently to 

 their death the buds rise to the surface, where, should the 

 winter be severe, they are frozen. Strangely enough, this 

 drastic treatment, contrary to being detrimental, as one might 

 expect, acts as a tonic. 



The following spring the outside case bursts, and the young 

 colony makes its appearance, ready to continue the good or bad 

 work left undone by its predecessors. 



Lastly the Polyzoa breed by fission ; spontaneous division of 

 the colony often occurs, and the daughter parts thus produced 

 increase by budding. There are six British freshwater 

 genera : 



Plumatella Alcyonella 



Cristatella Fredericella 



Lophopus Paludicella. 



Those most commonly found are members of the Plumatella, 

 a branched family, the colonists of which spread into long, 

 thin, branch-like forms covering the stems of aquatic weeds. 

 Each polype lives an independent life in its own sack, appear- 

 ing at intervals to wave its tentacles, so as to obtain some of 

 the various good things floating in its neighbourhood, for the 

 food of the Polyzoa mainly consists of decomposing organic 

 matter. The Plumatella have a crescent-shaped lophophore, fur- 

 nished with between forty and sixty tentacles. Perhaps it is not 



