144 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



capped and partly surrounded by from three to twelve very 

 thin but wide cells superposing each other (figs. 95, 96). 

 A characteristic feature of each one of these upper cells is 

 the situation of the nucleus, which is found on or near a 

 line passing perpendicularly from the cuticle through the 

 large central cell. There is no constancy in the size of the 

 nuclei. Beddard states that the central nucleus is very 

 large and that the other nuclei are small. While I have 

 found corpuscles in which the central nucleus was much 

 larger than the upper ones, in many instances the reverse 

 has been the case. The upper nuclei are generally of very 

 even size. 



When seen in a cross-section of the body of the worm 

 the sense-corpuscle is sac-like, generally higher than broad 

 (fig. 95). In longitudinal sections (fig. 97) the sense- 

 corpuscle is longer than high. The most interesting feature 

 of the sense-corpuscle is the structure of the large central 

 cell. Its size varies considerably, as may be seen by the 

 figures, but it is always larger than all the upper cells com- 

 bined. There are two very prominent characteristics of 

 this cell: the nucleus is situated in, and suspended by, a 

 diaphragm which forms a constant acute angle with the 

 base of the cell and the cuticle of the deric epithelium; 

 secondly the cytoplasm of the cell is laminated in a certain 

 and distinct manner (figs. 95-97). 



The central nucleus is evidently capable of extention and 

 contraction, as in some cells it is found to be much elon- 

 gated in the direction of the diaphragm, while in others it 

 is quite round. In some cells the diaphragm has the form 

 of a simple bar, dividing the vacuole into two equal parts ; 

 but in reality this diaphragm consists of a number of narrow 

 lamella which in the figure are only seen in cross-section. 

 The other ends extend to the opposite side of the vacuole 

 somewhat in the manner of a membrane stretched on a 

 drum. More strictly speaking, there are two central vacu- 

 oles separated by a diaphragm, and surrounding them is a 

 dense mass of peculiarly laminated cytoplasm. Cross-sec- 

 tions show that this lamination does not extend all around the 



