Vol. i] Bovard. — Sense Organs in Microscolex Elegans. 273 



cuticle. These areas above the organs measure from 6 to 35 

 microns in diameter. Their average size, however, is about 1") 

 microns. 



Lying within the membrane formed by the boundary cells, 

 are the sense cells proper. These are greatly elongated and nar- 

 rower at the ends than in the middle. The widest part is just 

 below the middle, which contains the nucleus. Their distal ends, 

 which are broader than the proximal, carry stiff bristles, which 

 extend through a short canal in the cuticle. The basal end of 

 the cell is very narrow, and runs out into one or two long pro- 

 cesses. Among the basal ends of these cells may be found low 

 cuboidal and sharply pointed columnar cells, which rest on the 

 basement membrane and project upward into the cavity of the 

 organ. Several of these have been observed to have long pro- 

 cesses running up along the sense cells, thereby suggesting 

 transition stages in their development. It is often difficult to 

 find the cell boundaries near the top of the sense organ, but in 

 the lower end the cells are quite far apart and sharply defined. 

 The internal structure of the sense organ of Lumbricus differs 

 from that of Microscolex in that in the former species the cells 

 have the same diameter at the distal and the proximal ends, and 

 stand entirely apart, not showing the close approximation at 

 the distal ends. Miss Langdon found no basal cells with pro- 

 cesses projecting up into the cavity of the sense organ, while in 

 Microscolex these were plainly seen. 



The cuticle has three kinds of openings. We note first the 

 largest openings, such as the nephropores (Plate XXV, Fig. 6), 

 the sexual openings, and the chaetae sleeves (Plate XXV, Fig. 

 5). When the cuticle is stripped off the cuticular sheathes of 

 the chaetea are removed with it, and in the preparations these 

 lie bent over and close to the cuticle, so that the position of each 

 chaeta is definitely marked on the metamere. The second class 

 of openings includes the sense areas (Plate XXV), which mark 

 the positions of the sense organs. These areas are circular, or 

 slightly oval, and thinner than the rest of the cuticle, and each 

 containing near its center openings for the sense hairs, which 

 became more scattered toward the periphery. The third kind of 

 opening is that of the gland cells of the epidermis. These are 



