^j 2 Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



circular or nearly so. Seen from above, it is brown, with a clear 

 round spot in the center. I take this to be, in part, an optical 

 effect due to transmission of light through a round opening on 

 the under side, through which the Amoeba projects, when its pseudo- 

 podia are extended. The pseudopodia are few in number; and 

 come out radially from the sides of the Amoeba. They are large; 

 and they are evidently extensions of the protoplasm, including 

 part of the endosarc. In this form there is a vertical axis connec- 

 ting a dorsal and a ventral pole. 



A Walking Cell. The pseudopodia of Arcella discoides 

 are somewhat changeable, both as regards thickness and length. 

 But in another cell, (fig. 4, pl. Ib), sometimes found in the sediment, 

 at the bottom of the aquarium in which the Amoebae live, the pro- 

 cesses corresponding to the pseudopodia of Amoeba have become 

 fixed; and assume the character of large cilia. 



In this Walking cell, which resembles a Paramaecium more 

 than an Amoeba, there is a distinct fore and aft polarity. At the 

 anterior end, and running along one side of the elongated body, 

 there is a groove bordered by short, thick cilia, evidently the 

 most primitive beginnings of a ciliated alimentary canal. Uni- 

 cellular algae are swept into this canal by the motion of the cilia, 

 and pass along the groove to the posterior end. 



I call this a Walking cell, because the few long cilia projecting 

 from the body of the cell are used more for Walking than for swim- 

 ming. The cilia are about equal in length to the diameter of the 

 body of the cell. At the posterior end, are two long cilia which 

 are divided at the end into three long prongs. The long cilia do 

 not move synchronously, as is usually the case in infusoria. They 

 move alternately in such a way as to present, under the micro- 

 scope, a good image of the movements of the limbs of a Walking 

 fly. This cell rarely swims ; but crawls over and between the 

 particles of sediment, somewhat as a fly would. 



I take these cilia to be a further development of pseudo- 

 podia, such as Arcella presents. The forked feature of the posterior 

 ones, suggests that such cilia may, in one sense, be considered 

 as the ,, Anlage" of the limbs of higher forms. 



I am aware of the difficulties arising from such an assumption 

 of homology between a unicellular and a multicellular organism. 

 But the question of homology in this case is not so important 

 as the fact that organs are developed in a cell, which perform 

 the same functions as similar organs in higher forms; and which 

 confirms the suspicion that functions in onecelled organisms may 

 be performed by structures resembling those of higher forms. 



I take these cilia to be connected at their base with the con- 

 tractu^ protoplasm of the cell. They are probably constructed 

 somewhat like the stalk of the Vorticella. The coordinated action 



