NOCTILUCA. 



[ 462 ] 



NOSTOC. 



Smith describes twenty -three species, 

 mostly removed from other genera in the 

 systems of Ehrenberg and Kiitzing. 



N. sigmoidea (PL 13. fig. 9; a, side view; 



b, front view). Frustules (front view) linear, 

 sigmoid, or arched, truncate, side view 

 straight or nearly so, attenuate, acute ; aqua- 

 tic; common; length 1-75". 



N. lanceolata (PL 13. fig. 10; a, front 

 view of frustule ; b, front view of single valve; 



c, side view of frustule). Frustules (front 

 view) straight, lanceolate, ends prolonged, 

 somewhat obtuse ; side view narrowly linear- 

 lanceolate, ends acute; marine; length 

 1-150". 



Fig. 10 a is too broad ; the form of the 

 frustules is best represented by 10 b ; 10 d 

 exhibits the two kinds of markings as seen 

 with the stops, &c. 



N. longissima (N. birostrata, Sin.) (PL 13. 

 fig. 11 ; a, side view; b, front view). Frus- 

 tules straight, narrowly linear-lanceolate, 

 ends produced into linear beaks, longer than 

 the intermediate portion; marine; length 

 1-70". 



N. acicularis (PL 13. fig. 13, right-hand 

 frustule). Frustules linear-lanceolate, some- 

 times sigmoid, ends beaked and straight; 

 aquatic, and brackish water; length 1-300". 



N. reversa (PL 13. fig. 12). Differs from 

 the last in having the ends bent at an angle 

 in opposite directions. 



N. gracilis (N. tania (?), Sm.) (PL 13. 

 fig. 13, left hand). Linear or slightly lan- 

 ceolate, with two spiral markings; ends 

 somewhat suddenly produced ; brackish 

 water; length 1-250". 



The spiral bands probably arise from the 

 frustules being twisted, and correspond to 

 the sutures; they are most distinct after 

 a red heat. 



BIBL. Smith, Brit. Diat. p. 37 ; Hassall, 

 Freshwater Algce, p. 435. 



NOCTILUCA, Suriray. A genus of ma- 

 rine animals, the systematic position and 

 structure of which is doubtful. 



N. miliaris is spherical or nearly so, with 

 a tentacle-like, transversely striated, and 

 curved process arising from it, and by means 

 of which it propels itself through the water. 

 The part to which the process is attached is 

 plicate and depressed, so as to render the 

 body somewhat bilobed; it has no carapace. 

 The body has been described as of gelatinous 

 consistence, and as surrounded by a smooth 

 or wrinkled membrane ; again, as consisting 

 of an air-bag. Its diameter has been esti- 

 mated at 1-1000", and as lying between 



1-50 to 1-30", the latter of which is probably 

 correct. 



It is phosphorescent, rendering the sea 

 luminous by night. 



BIBL. Suriray, Lesson's Acalephae ; Qua- 

 trefages, Ann. des Sc. nat. 3 ser. xiv.; Gosse, 

 Naturalist's Rambles, <^c. ; Krohn, Wieg- 

 mann'sArchiv, 1852 ; Huxley, Micr.Journ. 

 1855 ; Brightwell, Ann. Nat. Hist. 1850. vi.; 

 Pring, Phil. Mag. 1849. 



NOSTOC, Vaucher. The typical genus 

 of the Nostochaceac, distinguished from the 

 allied genera by the definitely formed hard- 

 ened pellicle or rind enclosing the fronds, 

 which are composed of a gelatinous sub- 

 stance (fig. 532), in which are imbedded 



Fig. 532. 



Nostoc commune. 

 Nat. size. 



numerous more or less beaded filaments 

 (fig. 533). The filaments are composed of 



Fig. 533. 



Nostoc cseruleum. 

 Filaments. Magnified 200 diameters. 



rows of cells (PL 4. fig. 7), .which increase 

 the length by repeated transverse subdivi- 

 sion ; here and there appear larger cells (a, 

 c) which appear brighter than the rest ; these 

 seem to be what Kiitzing calls the spermatia 

 or spermatic cells, but they more resemble 

 the vesicular cells of the allied genera. The 

 filaments break up after a time into short 

 fragments, which by cell-division produce 

 new filaments. Thuret has observed this 

 process in N. verrucosum ; he states that the 

 pellicle of the frond bursts, allowing the 

 gelatinous mass to escape, and the filaments 

 to spread abroad in the water; these are 



