238 -THE AMERICAN MONTHLY [October, 



vacuoles, and at one end a long slender flagellum siuTounded by 

 a cuticular collar or cup, recalling the smaller cup and flagellum 

 of N^ociiluca^ and somewhat less distinctly the flagellum of Peri- 

 diniiim. The colony of Codosiga is sessile, the members are 

 crowded together on the ends of ternately divided stems, which 

 bring the members up to common level. The manner of division 

 is shown in figure 20. Codosiga^ Noctihica^ Peridinium^ have 

 been selected to give an idea of the order Flagellata, the mem- 

 bers of which have fixed outline of body, no stony skeleton, and 

 one or more flagella. 



Paramecium aurelia (fig. 21) or some other of the numerous 

 species of Paramecium are sure to appear in the same standing 

 water with Amoeba and the other Protozoa already mentioned. 

 It is an elongate, exceedingly active creature. The body is covered 

 with a firm outer layer which is not separate from the protoplasm 

 beneath. The body is infolded on one side. It is covered with 

 cilia, all of the same size. These move the body and also move 

 currents of water into the cavity just mentioned, where, at a par- 

 ticular place, the food is engulphed. The nucleus is rod-shaped. 



Stentor polymorphus (fig. 22) is more rare than Parame- 

 cium. It is trumpet-shaped, the broad end is surrounded by cilia 

 of larger size, and those of the body are more minute. The 

 nucleus is shaped like a string of beads. Stentor lives in fresh 

 water, and is usually attached by the smaller end. 



Vorticella sp. indet (figs. 24, 25, and 26) is a fresh-water 

 animal found attached to immersed leaves. It lives in colonies. 

 Each member presents a bell-shaped body terminating a long and 

 slender stem. It is very sensitive and on the slightest disturb- 

 ance the bell becomes a sphere by the retraction of the rim shown 

 half completed in figure 25, and the stem is spirally coiled, thus 

 withdrawing the body quickly from the place of danger. The 

 normal condition of things is shown in figure 24. At such times 

 the contractile thread can be seen running up the stem. The body 

 is partly closed at the end but furnished with a groove which 

 leads into a deeper cup, the oesophagus. The rim is furnished 

 with strong cilia and the oesophagus is lined with the same. 

 Food is moved by them to the bottom of the oesophagus, where it 

 is engulphed. The nucleus is a curved rod. Reproduction is by 

 division. Figure 26 represents the act of conjugation in Vorti- 

 cella. In this case a smaller vorticella is produced In' division 

 which acquires a circle of cilia around the base. It then swims 

 freely through the water and meeting a second Vorticella attaches 

 itself and becomes gradually absorbed so as to finally entirely dis- 

 appear. This act of conjugation is of great importimce, for it 

 seems, from various observations, probable that by it the powers 

 of division are reinvigorated, powers which would otherwise 

 flag and ultimately result in death of the organism. 



Pyxicola affinis (fig. 23) is like / orticella and Stetttor a cil- 

 iated animal with the cilia terminal, but the body inhabits a chit- 



