206 FRESH WATER RHIZOPODS OF NORTH AMERICA. 



A central nucleus brought into view in an individual, by the action 

 of an ammoniacal solution of carmine, was finely granular, and about 

 0.0238 mm. in diameter. 



The exterior of the body of Acanthocystis chcetophora is profusely 

 invested with exceedingly delicate spinous rays, which are straight and 

 rigid, and remind one of minute acicular crystals emanating from a nuclear 

 centre. In strong, reflected light, these rays appear glistening white, and 

 they are silicious in composition. They are attached to the surface of the 

 body by little disks, which give to it a minutely mammillated appearance, 

 and are sufficiently numerous to form a complete scale-like armor to the 

 animal. 



The ray spines are of two kinds : a longer, stouter form, terminating 

 in an acutely notched extremity (figs. 1 , 2), and a shorter and more delicate 

 form, with a wide, furcate extremity (fig. 3). The longer, stouter spines 

 exhibit a dark axial line, apparently indicating a tubular condition. In 

 some individuals, the shorter and more delicate spines are absent. 



The pseudopodal rays of Acanthocystis chcetophora are numerous, and 

 of the same character as those of Actinophrys sol. Commonly, they are 

 difficult to distinguish among the forest of spinous rays, excepting where 

 they project beyond these. 



Commonly, the body of Acanthocystis chcetophora is invested with a 

 thick layer of protoplasm, distinguished chiefly from its being densely 

 pervaded by exceedingly minute, linear particles, which remind one of an 

 atmosphere of bacteria enveloping the animal. Usually, this dust-like 

 stratum includes completely the smaller furcate rays, and ascends in 

 pointed processes upon the longer ones to a variable extent. Sometimes 

 the exterior stratum, with its bacteria-like particles, is completely absent. 



Commonly, the body of Acanthocystis chcetophora is about U.0833 mm. 

 in diameter. The longer furcate spines measure about 0.1 mm. in length, 

 and appear as fine as the micrometric lines themselves. The smaller spines 

 are from a fifth to a third the length of the others, and much more delicate. 



Acanthocystis chcetophora occurs in the same localities as the ordinary 

 Sun-animalcule, and, though frequent, is not so common as the latter. It 

 likewise has nearly similar habits. At times it appears to remain quite 

 stationary, but mostly exhibits a slow gliding motion, and apparently so 

 passive that it seems to be induced by a feeble current of the medium in 



