1908] Robertson. — Incrusting Bryozoa. 273 



there seem to be two rinos of cilia at the oral rim, imcoimected 

 in the middle. The interior cavity is divided into three parts: 

 a median part or atrinm leading directly to the mouth, m. ; an 

 anterior atrium whose rim is surrounded by the anterior ring of 

 cilia and w^hich contains the pyriform, pyr., body; and a pos- 

 terior atrium into which the digestive tract opens, int. The 

 median atrium, known as the oral atrium, is deep and lined on 

 all sides with cilia which lash upward. Currents containing food 

 particles are thus set in motion toward the mouth, m., which 

 opens directly into a large stomach, stm., and this into the intes- 

 tine, int. In the intestinal atrium is a large gland-like body, 

 sue, which OstroumofiE ('85) first pointed out is the disk or 

 sucker so-called by which fixation of the larva takes place. Be- 

 side the sucker is the adductor muscle, add., of the shell. The 

 tuft of cilia at the apex extends from a cell plate known as the 

 retractile disk, re. d. Between it and the pyriform body there 

 extends a bundle of fibers, /?., in which movements of "contraction 

 are frequently visible. Protruding from the antero-oral rim, be- 

 low the pyriform body is a tuft of long stiff cilia, st. c, whose 

 movements are synchronous with the movements in the fibers 

 connecting the retractile disk and the pyriform body. Prouho 

 ('90) in investigating a similar fibrous strand in the larva of 

 Flustrella, a larval form very similar to Cyphonautes, ascribes to 

 the fibers connecting the retractile disk and the pyriform body 

 both a contractile and a nervous function, considering that the 

 fibers are of two kinds, muscle fibers and nerve fibers. Accord- 

 ing to Kupelwieser ('06) not only does this bundle of nervo- 

 muscular fibers connect the retractile disk and the pyriform body, 

 but a functional relation exists between the tuft of stiff cilia, 

 St. c, and this fibrous strand. The tuft of stiff cilia, this inves- 

 tigator considers, exercises an important sensory function in the 

 discrimination of food particles, and a mechanical function in 

 getting these particles into the food current passing into the 

 median atrium and thus into the mouth. The bundle of mixed 

 fibers partly effect, partly regulate the movements of the stiff 

 cilia in the performance of these functions. 



In swinuiiing, Cyphonautes moves in circles, generally tilted 

 so that the aboral side is forward, and half of the shell and con- 



