72 BEITISH FRESHWATER RHIZOPODA. 



produce a slight jerky motion of the body from side 

 to side. 



The nucleus is prominently situated, appearing in 

 some individuals as an irregularly -rounded body, 

 strongly refractive, and about 9 JJL in diameter. Schulze 

 remarks that it is surrounded by a clear space, and 

 that within its substance may be detected " a number 

 of minute globular, sharply -bounded clear spots, which 

 have the power of altering their positions." 



Usually two contractile vacuoles may be observed 

 imbedded in the densely-granular protoplasm near 

 the periphery, on each side. Their pulsations appear 

 to be very languid. 



The bacilliform spicules, of which mention has been 

 made, line the outer surface of the body in a thin 

 stratum, apparently imbedded in a mucous film. They 

 vary in number ; in some individuals so few as to be 

 hardly perceptible ; in others thick enough to justify 

 the specific name given to the organism. 



In water from a pond at Xorthen Etchells, Cheshire, 

 about the end of June, a form of Mastigamoeba occurred 

 which presented a remarkable variation from the type. 

 The posterior extremity, instead of being broadly 

 rounded, formed a circular expansion of ectoplasm, 

 finely granular, containing some small vacuoles, and 

 fringed with short radiating conical or acute pseudo- 

 podia, of very delicate structure. A few minute 

 spicules could be detected on the surface of this 

 appendage, but neither on the body nor on the pseudo- 

 podia proper were any visible. The pseudopodia, in 

 these abnormal examples, were more attenuated and 

 fewer in number than in the others, and at the same 

 time more pellucid. The flagellum was active in most 

 cases, seeming to perform the function of a tentacle. 

 The individuals were comparatively small, and generally 

 lighter in colour, and they had a wider margin of 

 ectoplasm. For the present we retain this (PL VI, f . 4) 

 as a variety M. aspera, var. cestriensis. 



