466 



THE AMERICAN NATURALIST 



[Vol. LV 



are arranged in whorls, one on the oral side, the other on the 

 aboral side (Fig. 1, or. wh.; Fig. 2, ah. wh.).' 



The oral whorl is the more extensive. In the oral groove 

 (Fig. 1, 0. gr.) the fibers run obliquely caudad to the eytostomc 

 where they turn and converge obliquely eephalad to the neuro- 

 motor center. From other parts of the oral surface they run in 

 gracefully curved lines directly to the neuromotor center. 



The fibers of the aboral whorl converge in a large apex on the 

 right, opposite and slightly posterior to the cytostome. Here 

 they dip into the endoplasm and run direet to the neuromotor 

 center. 



The entire periphery of the animal is supplied witli the diverg- 

 ing fiber ends of these two whorls. On the left side t]u)se of the 

 oral whorl meet those of the aboral whorl about midway between 

 the two sides. On the right the inner ends of the fibers of the 

 oral whorl mingle with those of the aboral whorl near the con- 

 verging apex of the latter. 



Two sets of fibers connect the organelles of the eytopharynx 

 with the neuromotor center. One, a fan-shaped set. runs in the 

 right wall of the eytopharynx to the anterior membranelle zone. 

 The other set consists of two fibers which run from the neuro- 

 motor center to the peristomal cilia around the cytostome and 

 meet in the posterior margin. From here they run in the oral 

 side of the eytopharynx and branch profusely into the posterior 

 membranelle zone and the eiidoplasm. This posterior zone, the 

 cilia of which beat in an opposite direction to those of the an- 

 terior membranelle zone, has not been previously described. 

 The cytopharyngeal fibers are heavier than the peripheral fibers 

 and may be seen in living unstained animals under oil immersion. 



The trichocysts are arranged with reference to tlie peripheral 

 neuromotor fibers in whorls. They reach the surface of papillse 

 which constitute interrupted ridges (Fig. 1, t. r.) . The cilia, 

 however, spring from longitudinal grooves. The grooves from 

 each side of the oral surface meet in a series of V's, the apices 

 of which lie in a Htic, the ciliary suture (Fig. 1, c. s.) which ex- 

 tefids obliijuely through this surface from the anterior to the 



(4) also found tli — ■ aii,l ridl...! i I:,.m! .•ili.iiy n.otl,.ts. 



