12 BULLETIN OF THE 



In Pbagocata the rhabditi are found in almost every portion of the 

 hypodermis, there being only one region from which they are altogether 

 absent, viz. around the gonopore, where they are gradually replaced 

 by many subcutaneous glands, which open to the exterior in a broad 

 circular area surrounding that oriiice. They are present around the 

 oral opening, even up to the aperture, where they abruptly cease. 

 They are most abundant in the middle line on the back, becoming 

 gradually fewer toward the sides and anterior end, but they are again 

 abundant on the ventral surface. They are found over the eyes, and in 

 the epithelium of the two anterior sense organs, where they are well 

 developed but few in number. Iijima ('84, p. 371) has stated that they 

 are wanting in this region in the case of D. lacteum, but are present in 

 Planocera polychroa and Polycelis tenuis. He has also shown that in 

 the case of I), lacteum they are unusually abundant in the region of the 

 genital orifice, both in the epithelium and in the parenchyma, and sup- 

 poses that they have a sexual significance as urticating organs, the 

 " Liebesfeile " of Schneider ; but their absence in this region in Phago- 

 cata precludes the assumption that they have in this species any such 

 function. 



The rhabditi are all of one kind, but they vary in size. The varia- 

 tions are not local, different sizes occurring wherever rhabditi are found. 

 Some are as long as the hypodermis cells, while others are comparatively 

 short; they vary from 1.5 /a to 16 /a in length. There is an interesting 

 correlation between the thickness of the hypodermal layer and the size of 

 the largest rhabditi ; those of the thin hypodermis of the ventral surface 

 are invariably smaller than those of the dorsal side. Each is spindle- 

 shaped, and the outer end is slightly more pointed than the deep end. 

 They stain intensely in the carmine dyes, and then appear perfectly 

 homogeneous ; but when stained in Orth's picrocarminate of lithium 

 with an excess of the picric acid, they take on a bright yellow color, 

 and appear more or less swollen and distorted, according to the length 

 of time the dye is allowed to act. Often they have the appearance of 

 hollow capsules filled with granules, or containing a few irregular re- 

 fractive lumps (Fig. 9). It was probably the swollen and altered rhab- 

 diti that Moseley mistook for gland cells. The peripheral portion of the 

 substance of the rhabditi is not affected by the reagent as the contents 

 are. This outward unaltered portion presents the appearance of a cap- 

 sule, or thick membrane, with a double contour. Moseley says of his 

 glandcells, "The cell appears to have a double wall, for an irregular 

 crumpled membrane is seen often within it." 



