48 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



Certain specimens met with from time to time, and regarded as pertain- 

 ing to Amoeba proteus, but presenting - either more or less peculiarity, or 

 some point of special interest connected with the history of the animal, 

 may here be described. 



A specimen obtained in the spring of the year from the ooze of a ditch 

 when first seen had the appearance represented in fig. 25, pi. IV. It was 

 globular, about 0.2 mm. in diameter, and projected a number of digitate pseu- 

 dopods in different directions. Besides the usual contents, in the vicinity of 

 the large contractile vescicle, there were observed half a dozen granular 

 balls from 0.016 to 0.024 mm. in diameter. The granules within the balls 

 exhibited an active swarming motion, reminding one of the rapid movements 

 of spermatozoids in higher animals. The nature of these granular balls I 

 failed to determine, but suspected they might really constitute male elements 

 of the Amoeba. The individual after a little while moved off in the manner 

 usual with Amoeba proteus, assuming a dendritic form. The nucleus was 

 distinctly, coarsely, and uniformly granular. The contractile vesicle ex- 

 panded to the extent of iVth of a millimetre in diameter, and would col- 

 lapse in two seconds of time. Sometimes it would reappear as two, which, 

 after expanding to a certain extent, would unite into a single one. After 

 keeping the specimen the greater part of a day, it was finally lost without 

 my having learned anything further in regard to the granular balls con- 

 tiguous to the contractile vesicle. 



I have repeatedly met with Amoebae, which I have supposed to pertain 

 to the species under consideration, though they presented sufficient pecu- 

 liarity to make the reference uncertain. 



A not unfrequent form is such as are represented in figs. 22, 23, and 

 24, pi. IV. Comparatively active, in creeping on flat surfaces, the animal 

 commonly presents a prolonged, somewhat triangular outline ; straight or 

 curved, with the broader extremity in advance, and spreading into a variable 

 number of conical-pointed pseudopods. These undergo frequent, but slow 

 change, and in their extension do not receive so much of the coarser con- 

 stituents of the endosarc as usual in more characteristic forms of Amceba 

 proteus. The posterior end of the body is narrow and blunt, simple or 

 papillose, and sometimes is produced into a brush or fringe of rather long 

 villous processes. The animal is greedy in habit, and usually contains 

 much food, consisting of alga?, mingled with other constituents of the 



