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



Surrounding the outer border of the cup just without the 

 insertion of the outer row of cilia is the so-called velum of 

 Fabre-Domergue (1888). In the living Licno-phora it 

 appears as a delicate homogeneous membrane 8 ytt to 10 yu- 

 in width (fig. 76, v^, v^) , made up of two overlapping parts 

 as figured by Wallengren for L. auerbachii. In radial sec- 

 tions of the disc the velum appears as a loop of pellicula, 

 often, but not always, containing finely granular cytoplasm 

 (figs. 4, V, 13, 14, v'). The velum may function when 

 the animal is attaching itself to its host to secure more 

 perfect suction, but it is certainly not closely pressed against 

 the host afterwards, as such pressure would prevent the con- 

 stant free movement of the ciliary membranes. No definite 

 movement of the velum itself has been observed, except a 

 constant vibration in unison with the ciliary membranes. 



Connected with the smaller neck fibre at its outer end 

 and apparently moved by its contraction is a vibratile mem- 

 brane (figs. 1,- e and 3, <?), consisting of an extensible 

 fold of pellicula reaching from the tip of the fibre in the 

 left hand margin of the cup along the left margin of the 

 neck groove to a point near its termination in the mouth. 

 The membrane is raised and extended by an outpushing 

 and elevation of the extremity of the fibre, given a for- 

 ward flapping movement as the fibre is drawn inward and 

 downward, and disappears from view, being somewhat con- 

 tracted laterally, and folded forward over the ventral neck 

 groove (fig. 77, a, b, c, d). When the extremity of the 

 fibre (fig. 77, b) reaches its highest point, the membrane 

 is very tense and its margin is a strong definite line; as the 

 fibre is lowered, the margin becomes indistinct and the 

 whole membrane vanishes. The appearance and disappear- 

 ance of the membrane is seen both when the infusorian is 

 attached and feeding, and when it is swimming. The move- 

 ment is quite rhythmical but the rate varies greatly at differ- 

 ent times, being much greater in swimming. When the 

 Licnofhora is at rest, this membrane is often extended for 

 some time, either motionless or waving slowly, sometimes 

 at one end, sometimes at the other, and again along the 

 whole edge. The vibration certainly produces a current 



