14 PROTOZOA. 



8. The stalk is composed of a sheath, which is continuous with 

 the cuticle of the body, and, within the sheath, the contractile 

 axis or myoneme, which is continuous with the body ectoplasm. 

 Notice that this myoneme is situated within the sheath in a 

 very loose spiral, and that the stalk quickly contracts into a 

 close spiral when the animal is stimulated. Observe also the 

 manner in which the peristome folds over simultaneously with 

 the contraction of the stalk. What purpose does the contrac- 

 tion of the stalk serve? 



Vorticella is distinguished from its allied genera by its sim- 

 ple unbranched stalk and also by the spiral form assumed by the 

 contracted stalk. In which order of the Ciliata does the cilia- 

 tion of Vorticella place it? Compare with Zoothamnium. 



Make a drawing of an expanded individual and a sketch to 

 show the condition when contracted. (See Doflein, Fig. 816, p. 

 867.) 



9. Study, by means of finely powdered carmine, the vortex 

 currents set up by the cilia. Note how the particles are collected 

 in the gullet, and at intervals are forced in rounded masses into 

 the endoplasm to form gastric vacuoles. Is there a definite 

 circulation in the endoplasm? 



10. Endeavor to find several stages of reproduction by divi- 

 sion. 



Large fresh-water species of Vorticella are preferable for 

 study, but marine species may be substituted when necessary. 

 If time and material permit, study Lichnophora, a marine peri- 

 trichous form parasitic on Crepidula. (See Calkins' Protozoa, 

 p. 203.) 



Schroder: Beitrage zur Kenntnis von V. monilata. Arch f. Protist.. 7, 

 1906. 



OXYTRICHA. 



Infusoria belonging to the genus Oxytricha, or the genera 

 Stylonychia, Pleurotricha, Euplotes, etc. (see Doflein, Fig. 136, 

 p. 138), may be used for the following study. These forms 

 belong to the order Hypotrichida. Hypotrichous forms are 



