RHYTHMICAL ACTIVITY IN INFUSORIA. 307 



mical back-and-forth movements. Even very small pieces, less 

 than one sixteenth of the body, show the same regular rhythm 

 and the same correlation of ciliary and contractile activity. 



Dileptus gigas. — Dileptus gigas commonly adheres to the sur- 

 face of some solid object and waves its long proboscis-like ante- 

 rior extremity or neck about in an anti-clockwise direction. The 

 surface of the body is quite sticky, as is shown by the fact that 

 it adheres readily to any object brought in contact with it. The 

 slender extremity in its movement about in a circle executes 

 many twists and curls in more or less irregular ways. These 

 movements may be very vigorous or they may be very slow, but 

 they scarcely ever entirely cease. The slender neck is very ex- 

 tensile and may be elongated to three or more times its length 

 when in a contracted state. 



Dileptus often executes short forward and backward movements 

 at tolerably regular intervals. During its movement forward the 

 body elongates, and while gliding backward it widens, showing 

 the same correlation of contractility with the direction of the beat 

 of the cilia that occurs in Loxophyllum meleagris. The backward 

 and forward excursions vary exceedingly in length. Frequently 

 they are exceedingly short. Even when the organism remains 

 attached in one place the body undergoes more or less regular 

 elongations and contractions while waving about the anterior ex- 

 tremity. There is a rhythm here much as in the preceding 

 species occurring quite independently of external stimulation. 

 The posterior third of the body when severed from the rest still 

 undergoes elongations and contractions, although in a somewhat 

 lessened degree. In larger pieces the rhythm of movement is 

 more manifesto 



Lachrymaria olor. — This interesting species resembles Dileptus 

 gigas in its general behavior as well as its external form. Its 

 long flexible neck is kept continually waving about, but the ex- 

 tensions and contractions of its body do not occur so regularly 

 as in the preceding species. 



Vorticella. — Vorticella frequently shows quite regular rhythmic 

 contractions without an apparent external cause. The peristome 

 with its membranellae is folded in and the stalk contracts into a 

 spiral form. In a short time the spiral straightens out, the peri- 



