346 University of California Puhlications in Zoology [Vol. 18 



other than rounded along its entire anterior edge. It extends across 

 the anterior of the animal the width of the cytostomal field and in its 

 development it is seen that it is produced by the forward growth of 

 the dorsal wall of the cytostome. At each end of the lip the lateral 

 edges of the cytostome are continued forward and join the anterior 

 edge of the lip (1., fig. A). In examining the lip in either dorsal or 

 ventral view it is seen that it contains many small vacuoles and a struc- 

 ture in the form of a peculiar lattice work, which will be described 

 later as a tactile sense organ. When viewed in longitudinal section 

 the lip is seen to be wedge shaped, the heavy cuticle of the dorsal and 

 ventral sides joining at the margin in an acute angle in such a way 

 as to give the lip great rigidity. In a study of the living organism 

 its has not been possible to note any movement of this lip. Such a 

 lack of flexibility gives no indication that the lip functions either as 

 a locomotor organ or as a structure concerned in food getting. On 

 the other hand its position at the anterior end and the lattice work 

 structure which it contains, point to the fact that the lip may serve 

 as a tactile sense organ, probably in conjunction with the series of 

 membranelles which lie dorso-posteriorly to it. 



In the anterior half of the animal is the Cytostomal field, which 

 occupies about one-fourth of the whole ventral surface (cyt., fig. A). 

 This field is approximately triangular and is formed as a deep depres- 

 sion of the ventral side. On the left the cytostomal field is bounded 

 by the series of cytostomal membranelles, while on the right it is 

 abruptly joined by a cavity which deepens dorsally and extends under 

 the right ventral field for a distance of about fifteen microns or one- 

 sixth the width of the body at its widest part. Anteriorly the roof 

 of the cytostome is continuous with the projecting anterior lip. Pos- 

 teriorly the cytostome narrows and leads into the ciliated pharynx, 

 which curves rather sharply to the right and leads by a narrow tube 

 into the endoplasm near the median line slightly posterior to the 

 middle point of the body. By a twist of the series of membranelles 

 the posterior left half of the cytostome is ciliated. The twist so turns 

 the membranelles that the cilia point toward the cavity of the cj^to- 

 some, instead of at right angles to the ventral surface as they do 

 anteriorly. Posteriorly these membranelles extend into the pharynx, 

 forming the cilia on the left side of the pharynx. Similar cilia are 

 also found on the right hand surface of the pharynx, thus making the 

 anterior portion of the pharynx completely ciliated. A study of the 

 living animal shows that the cilia of the membranelles beat in such 



