LIFE HISTORY OF TWO RARE CILIATES 355 



Extending from end to end of 'the body are many delicate 

 longitudinal striations, marking the Hnes of insertion of the cilia. 

 These organs are distributed uniformly over the body and are 

 of equal length except in the oral region where those bordering 

 the mouth are somewhat longer. The body is covered by a 

 thin but firm cuticle which gives it its permanency of form allow- 

 ing at the same time the greatest flexibihty. In section the 

 cuticle is seen as a pale area, bounded by a definite line surround- 

 ing the more opaque central portion (fig. 2). The p"rotoplasm 

 immediately underneath the cuticle, constituting the cortical 

 • plasm, appears somewhat denser than that toward the center, 

 although there is not a distinct line of demarcation between 

 the two areas. The entire protoplasm is finely granular. 



As the animal swims rapidly through the water, rotating on 

 its long axis, the anterior end of the body, wh'ch is extremely 

 flexible, is in constant motion, bending upward, downward and 

 from side to side as though feeling its way. Owing to this con- 

 stant change of position, this region continually presents new 

 aspects, as is shown in sketches of many of the total preparations 

 as well as in figures 13 and 17. The mouth, a narrow sHt, sub- 

 terminal in position, is bounded by the thickened edges of the 

 truncated tip. Maupas thought the mouth-opening was limited 

 to the extreme posterior part of the oblique edge, but I have 

 found it to extend the entire length of the truncated end. The 

 nature and extent of the mouth can best be determined during 

 the act of feeding. Spathidium is a predatory form, swimming 

 actively about as though in search of prey. The moment the 

 anterior end of the body comes in contact with a Colpidium, 

 all motion in the latter ceases. Spathidium twists and bends, 

 its flexible body until the smaller diameter of Colpidium is paral- 

 lel to the truncated edge; the mouth opens, the thickened lips 

 surround the small ciliate which passes slowly down into the 

 body of the captor, the entire process occupying not more than 

 five minutes. 



Small spindle-shaped bodies, which in fixed specimens appear 

 as closely crowded fine lines, are imbedded in the thickened 

 rim of the mouth directly underneath and at right angles to 



