96 PROCEEDINGS OF THE ACADEMY OF [Feb., 



thickness of the hypodermis of this region; the point of the wedge 

 being directed inwards (figs. 19 and 20). The nuclei of these cells are 

 situated near their inner ends, and often compressed laterally. 



The ventral ciliated areas of the trunk and head are essentially 

 similar in structure. That of the trunk contains both ciliated and 

 non-ciliated cells in the proportion of about two to one (fig. 28). The 

 outer surfaces of these cells are irregularly polyhedral and not elongated 

 in the direction of the long axis of the body, as Schimkewitsch (1895) 

 has described them in D. vorticoides. The cells composing the ventral 

 ciliated strip are cubical or columnar near the midline, but toward the 

 outer margin of the strip the cell walls slant inwards, so that the cells 

 here have the form of pyi^amids or truncated cones, as illustrated in 

 fig. 14. 



The nuclei of the cilia-bearing cells resemble those of the non-ciliated 

 supporting cells. The cytoplasm of the ciliated cells is also finely 

 alveolar. Embedded in the cytoplasm, at a short distance from the 

 cuticle, are the end knobs of the cilia. These are oval in form, separ- 

 ated from one another by a distance of about 1 /.i. From the outer 

 ends of these arise the cilia, w^hich pass to the distal surface of the cell 

 and, piercing the cuticle, reach the exterior. The inner ends of the 

 knobs are attached to the intracellular fibrillse usually present in cilia- 

 bearing cells ; these have the appearance, in the best preserved material, 

 fixed in Flemming's fluid, of true fibrils, homogeneous in structure. 

 These fibrillse are exceedingly conspicuous in material fixed in sublimate, 

 appearing in such preparations as tapering rods (figs, 6, 7, and 9). 

 They pass inward to the base of the cell, and do not always converge 

 toward the nucleus. In some cases two or more fibrillas may be seen 

 to join together, and finally to terminate on the basement membrane 

 at a considerable distance from the nucleus, as seen in the middle cell 

 in fig. 14. To these fibrillse, which are alwaj^s more or less intensely 

 stained, the ciliated cells owe largely their darker aspect, as compared 

 with the non-ciliated supporting cells. 



The hypodermis, as already noted, is everywhere covered externally 

 by a cuticle. The latter is refractive, nearly homogeneous, or with 

 faint striations parallel to its surface. Its thickness ranges from ca. 

 0.9 n on the ventral surface of the trunk to ca. 1.1 /x on the ventral 

 surface of the head, where the hypodermis also reaches its maximum 

 thickness. 



Gland Cells. — ^The hypodermis is very rich in unicellular glands, 

 most of which are of large size relative to that of the supporting cells. 

 These glands are of three kinds or types; those of the first two types 



