NAILS. 



[ 453 ] 



NAVICULA. 



tlie anterior portion of the root, the poste- 

 rior part of the body, and the lateral mar- 

 gins of the nails, terminating in a fine layer. 



Fig. 511. 





e • '^WS^ilil^^^^---^ 



d 









/ 



f 



A 



a 



Transverse section of the body of the nail. A, cutis of 

 the matrix. B, rete mucosum of the nail. C, epidermis 

 of the same, or proper nail. «, plates of the matrix ; 

 b, plates of the rete mucosum of the nail ; c, ridges of 

 the proper substance of the nail ; d. deeper perpendicular 

 cells of the rete mucosum of the nail ; e, upper flattened 

 cells of the same ; /, nuclei of the cells of the proper 

 nail. 



Magnified 250 diameters. 



Fig. 512. 



(t 



Laminse of a nail after boiling with solution of cau- 

 stic soda or potash. A, side view. B, surface view, 

 rt, cell-membranes ; 6, nuclei seen from above ; c, the 

 same in side view. 



Magnified 350 diameters. 



which is, however, nowhere directly conti- 

 nuous with the substance of the nail. 



BiBL. Kolliker, Mikrosk. Anat. ii. and 

 the Bihl. therein. 



NAIS, Mull. See Naidina. 



NARCOTINE. See Alkaloids, p. 25. 



NASSULA, Ehr. — A genus of Infusoria, 

 of the family Trachelina. 



Char. Body covered with cilia arranged 

 in longitudinal rows ; mouth surrounded bv 

 a cone of rod-like teeth ; no proboscis nor 

 ear-like processes. 



The gastric sacculi of these animals fre- 

 quently contain a violet-coloured liquid, de- 

 rived from the solution of partly digested 

 Oscillatorice. 



N. elegans (PL 24. fig. 45; h, teeth). 

 Body cylindrical or ovate, somewhat nar- 

 rowed in front, very obtuse at the ends; 

 white or greenish. Aquatic; length 1-144 

 to 1-120". 



iV. aurea (PI. 24. fig. 46). Body ovate- 

 oblong, subcylindrical, golden-yellow, very 

 obtuse at the ends. Aquatic; length 1-120". 



N. ornata. Brounish green. 



It is questionable how far this genus is 

 difi^erent from Chilodon. 



BiBL. Ehrenberg, Jw/ms. p. 338 ; Stein, 

 Infus. p. 248. 



NAUNEMA, Ehr.— A genus of Diatoma- 

 ceae, no longer retained. 



BiBL. Ehrenberg, J/?/?is. 233 ; Kiitzing, 

 Bacill. and Sj). Alg. 



NAVICULA, Bory.— A genus of Diato- 

 macese. 



Char. Frustules single, free; valves ob- 

 long, lanceolate or elliptical, sometimes mth 

 the ends narrowed and produced, rarely 

 constricted in the middle, furnished with a 

 longitudinal line or keel, and a nodule in 

 the middle and at each end; sm-face of 

 valves covered mth depressions or dots ar- 

 ranged in transverse or slightly radiating 

 rows, producing an appearance of lines, 

 although both dots and lines are often invi- 

 sible by ordinary illumination. 



The valves are usually symmetrical, and 

 the keel median, but in two species the keel 

 is sigmoid and the valves insequilateral. 

 Sometimes the keel is double. There is 

 mostly a httle space between the rows of 

 dots (PL 11. fig. 8), so that these readily 

 exhibit transverse lines or striae by unilateral 

 oblique light ; but sometimes they are pretty 

 uniformly chstributed, as in many of the 

 species belonging to the first section of Gy- 

 rosigma. 



The species or forms are very numerous. 



