NIERSTRASSIA FRAGILE. 235 



indistinct cell boundaries. The ventral section, on the other hand consists 

 of high, ciliated elements filled with a darkly staining, granular secretion. Close 

 to the outlet and extending a short distance along the mid-ventral line of the 

 rectum the cells become lower and the secretion changes, in a fully developed con- 

 tlition, to a granular, highly refractive, yellowish product not effected by haema- 

 toxylin. The cells of the seminal receptacles are columnar, and the secretion, 

 consisting of droplets of varying size, is of a lavendar tint. Multitudes of 

 sperms are crowded against their free surfaces and in many cases have produced 

 a vacuolation and even disintegration so that spermatozoa may enter such cells. 



Nierstrassia fragile, s]i. nov. 



Eleven specimens of this species, all unattached, were dredged off the coast 

 of New Jersey (Sta. 2588A) at a depth of 479 fms. where the bottom consisted 

 of green mud. The smallest measures 2.5 mm. by 0.75 mm., while the largest 

 is 5 mm. long by 1 mm., the greatest thickness. This material, very well pre- 

 served, was taken in 1885, and for over twenty years remained in an ordinary 

 cork stoppered bottle so that its yellowish brown tint is probably due to tannin. 

 A silky layer of delicate spicules, rather easily dislodged, gives the animal a 

 hght frosted appearance. While the spines adjacent to the ventral furrow over- 

 arch it the greater number are directed diagonally away from the furrow in a 

 postero-dorsal direction, those along the mid-dorsal Une meeting each other 

 without, however, forming any marked keel. While a dorso-terminal sense 

 organ appears to be present the obliquity of the sections (the posterior end of 

 the longitudinally sectioned specimen was lacking) and a number of small 

 folds in the hypodermis renders it difficult to definitely decide this point. 



In some respects the hypodermis, cuticle, and single layer of spines show 

 a striking resemblance to the same elements in species belonging to Chaetoderma. 

 The spicules show this most clearly, having the characteristic leaf-hke form with 

 a longitudinal keel. By far the greater number of hypodermal cells (Plate 6, 

 fig. 2) are unmodified more or less cubical elements. In some instances a small, 

 compact mass, attached to the base of some of the spines, may represent a 

 degenerate spicule-matrix cell, but in most instances these have disappeared. 

 At rare intervals slender cells, possibly sensory, occur among the larger hypo- 

 dermal elements but no especial nerve supply has been detected. No structures 

 corresponding to papillae are present, the general appearance of hypodermis and 

 cuticle over the body being represented in the drawing (Plate 6, fig. 2) . 



The outlet of the anterior pedal gland consists of a simple, hemispherical 



