138 



SCIENCE-GOSSIP. 



accompanied by numerous micronuclei. The 

 motion is somewhat quick and rotatory. The length 

 may be as much as 1-5 miUimetres. The body is 

 colourless or brownish. 



The species occurs mostly in fresh water, but 

 has been found in the sea. It is synonymous with 

 Leucophrys patula of Cienkowsky. 



Family Spirostomidae. — " Animalcules free- 

 swimming, usually more or less flattened, rarely 



Fig. 28. — Bursaria truncatella ( x 75). 



pe, peristomial groove ; ad, adoral band of cilia ; gr, groove 



leading mouth ; ma, macronucleus. 



cylindrical, often attenuate; peristome field excavate, 

 extending along the left side of the ventral surface, 

 from the anterior extremity towards the centre of 

 the body ; the oral aperture locate in the angle 

 formed by the posterior border of the peristome ; 

 larger adoral cilia forming a right winding or 

 dextrotropous spire, continued along the entire 

 cuter margin of the peristome field, or confined to 

 the posterior portion only of that area ; the inner 

 border of the peristome occasionally bears an 

 undulating membrane." 



Spirostomum amlignum Ehrenberg, is cylindrical 

 in shape, and in most cases has both its ends 

 equally rounded ; sometimes, however, the hinder 

 end is truncated, or very much narrowed and 

 forming a kind of tail. The length is about 

 sixteen times the breadth. The animal is of large 

 size, being often as much as 3 millimetres long, 

 and is thus quite visible with the naked eye ; by 

 reflected light it looks like a small piece of silver 



Fig. 29. — Spirostomum amlignum ( x 100). 

 ma, macronucleus ; ad, adoral band of cilia ; oes, oesopha- 

 gus ; cv, contractile vacuole. 



thread. The body substance is in itself colourless, 

 but it may be coloured green through the presence 



of zoochlorellen, which starts at the anterior end, 

 and is continued often a good way past the middle. 

 Its breadth depends on the state of contraction of 

 the animal. From its posterior end starts a short 

 oesophagus. The adoral cilia run along the left 

 side of the peristome, and end in a spiral coil in 

 the oesophagus. There is no undulating mem- 

 brane. There is one very large contractile vacuole 

 at the posterior end, with which is connected a 

 collecting canal running nearly the whole way 

 down the back ; the anus is at the hinder end. 

 The anus is oval in shape and more or less central 

 in position ; many micronuclei are present. The 

 body surface is marked with very distinct spiral 

 striations. The animal lives in fresh water, and 

 moves by the action of its cilia, or by a worm-like 

 twisting and turning. It encysts itself in a lens- 

 shaped cyst formed of concentric layers. 



Family Stentoridae. — " Animalcules free-swim- 

 ming, or temporarily adherent, highly elastic and 

 contractile, more or less elongate and cylindrical ; 

 often inhabiting, either singly or socially, a mucila- 

 ginous or indurated sheath or lorica ; the entire 

 frontal border embraced by the peristome; the 

 peristome field circular, or produced into a single 

 central spiral or two lappet-like lateral prolonga- 

 tions ; oral aperture perforating the margin or 

 deeper confines of the peristome field ; larger adoral 

 cilia or cirri describing a complete dextrotropous 

 or right winding spire ; anal aperture situated 

 anteriorly immediately beneath the peristome." 



Stentor niger Ehrenberg, when fully expanded, is 



Fig. 30. — Stentor niger ( x 300). 

 /, left limb of peristome ; r, right ditto ; mth, mouth ; cv, con- 

 tractile vacuole ; at, anterior collecting canal of contractile 

 vacuole; ^c, posterior ditto ; »)irt, macronucleus. 



trumpet shaped ; the anterior end is broad and 

 truncate, the posterior end tapers off to a narrow 

 rounded extremity ; when contracted it is bag 

 shaped, or pear shaped. It is sometimes free- 

 swimming, sometimes sedentary. In the latter 

 case it attaches itself by its narrow hinder end. 

 The peristome runs almost completely round the 

 anterior border, its left end is folded in a spiral 

 fashion, and leads to the oral aperture ; the right 

 limb is free and raised considerably above the 



