6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



a connecting stalk or neck. The attachment disc is very 

 constant in form and size, while the oral disc is continu- 

 ally varying in outline; the stalk is exceedingly contractile 

 and so extensible that at times it reaches the length of one- 

 third that of the oral disc, and again contracts so as to 

 bring the two discs in contact, tangent to each other. 



In swimming the two discs are at right angles to one 

 another, but at rest they most often lie in parallel or oblique 

 planes (figs. 2, 3 and 68). 



In fixed specimens the length of the body, measuring 

 across both discs without cilia, varies from 67 yu. to 96 /i. 

 One very large specimen with stalk much extended, proba- 

 bly approaching division, measured 180 yu- alive (fig. 69). A 

 slight general contraction of all parts of the body occurred 

 with all methods of fixation, least with formalin. 



In the living respiratory tree the infusoria are seen 

 attached to the membrane and either swinging the oral disc 

 about now this way, now that, the attachment disc being 

 fixed; or more commonly rotating the whole body on an 

 axis passing through the center of the attachment disc at 

 right angles to the plane of attachment, in a direction oppo- 

 site to that of the oral spire (fig. 70). 



When set free in a watch-glass or on a slide the infusoria 

 swim very rapidly, attachment disc forward, with two char- 

 acteristic movements: (i) a rotary and a forward move- 

 ment combined, the peristomal cilia producing the rotary 

 movement and the ciliary membranes of the attachment 

 disc the forward movement; (2) an occasional more or 

 less periodic darting forward, in which contraction and 

 expansion of the stalk seem to be the motive power. They 

 also glide along the cover-glass as they rotate when 

 attached, and have been seen to run over a portion of the 

 respiratory tree with the cilia of both discs downward, 

 showing something of the agility of Trtchodhia ^ediculus. 



Structure and General Biology. — Licnofhora like most of 

 the Ciliata has a delicate structureless pellicula (Schultze), 

 not distinguishable in life, but readily separated from 

 the cytoplasm by macerating fluids and by many fixing 



