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CHAPTER XIII. 



THE TANGANYIKA POLYZOAN. 



An examination of the shells dredged up in Lake Tan- 

 ganyika, upon which there were visible organic incrusta- 

 tions, has revealed the fact that, besides sponges, the lake 

 fauna presents at least one species of polyzoan. The organ- 

 ism in question was first observed upon a Paramelania shell, 

 which had been dredged in about twenty fathoms of water 

 off the east coast, and upon the surface of which there was 

 visible a cellular incrustation, looking, under a lens, very 

 like a Flustra colony, but somewhat more irregular. More- 

 over it would be seen that the tubes of the cells were pro- 

 longed outwards and of considerable length. The colony 

 covered about a square inch of the shell, and upon others 

 there were subsequently found smaller colonies and indi- 

 vidual groups of two or three cells. In all cases, however, 

 they presented the irregular branched outline seen in the 

 figure given on page 296, the organism tending to form 

 a loose mat covering the surface upon which it grew. 



This polyzoan is gymnoleamatous, and is consequently of 

 great interest, since up to the present time only a very few 

 forms of gymnoleamata, Paludicella Victorella and the like, 

 have ever been found in fresh water. The Tanganyika 

 species does not correspond, however, with any of the 

 above forms, and it is of further interest, since it presents 



