NAIDINA. 



[ 451 ] 



NAILS. 



the fertile ramules being swollen in the 

 middle. 



BiBL. Harvey, Brit. Mar. Alg. p. 152. 

 pi. 20 D, Phyc. Brit. pi. 38; Greville, Alg. 

 Brit. pi. 16. 



NAIDINA. — A family of Annulata, of the 

 order Setigera. 



Char. Body worm-like, distinctly seg- 

 .mented, without suckers or soft leg-like 

 appendages ; segments furnished with par- 

 tially retractile bristles or setse, excepting 

 the three or four first ; head distinct from 

 the body. 



Animals aquatic, living among aquatic 

 plants, or burro\^ing in mud. Sexes di- 

 stinct ; propagation by ova and by sponta- 

 neous transverse division. The bristles are 

 moved by muscles, and answer the purpose 

 of legs. They are situated on the upper or 

 under surface of the body, mostly in rows. 



Nais, Mlill. Four anterior segments with- 

 out upper bristles. 



N. Scotica, Johnst. Body cylindrical, 

 ends obtuse, the anterior smooth and cylin- 

 drical, the portion behind it provided with a 

 double row of thin tufts of prickles, some of 

 them composed of several bristles, shorter 

 than the diameter of the body ; mouth and 

 anus terminal ; no proboscis. Length 1". 



N. serpentina [Serpentina quadristriata). 

 Body cylindrical, not flattened in front; 

 head snake-like, with a produced lower hp ; 

 eyes two, upper bristles subulate, lower 

 forked or uncinate. Length about \^". 



The lower bristles have a globular swel- 

 ling below the middle ; segments eighty to 

 ninety; head with four dark transverse 

 bands. 



N. prohoscidea [Stylaria lacustris). Body 

 cylindrical, flattened in front; first four 

 segments divided hy a stricture from the 

 body, the first, or head, being prolonged 

 into a filiform proboscis ; eyes two ; upper 

 bristles simple, lower forked. Length about 



1-0" 



Found on the roots of aquatic plants. 

 Middle segments nearly twice as broad as 

 long, regularly decreasing backwards ; upper 

 bristles twice as long as the width of the 

 body, the lower uncinate, with an incisure 

 about the middle. 



ChcBtogaster, Baer. All the segments 

 without upper bristles. 



C. vermicularis. Body cylindrical, trun- 

 cate in front ; eyes none ; mouth terminal ; 

 setse bifid. Length about 1". 



Found amongst Lemna, in ditches, and in 

 the respiratory chamber of the Lymneidae. 



We may append a notice of a very com- 

 mon setigerous Annelidan, which is perhaps 

 Tubifex rivulorum; if so, it has been incor- 

 rectly described, and we cannot identify it. 



Body annular, but not divided into seg- 

 ments, although an appearance of this is 

 given by the existence of numerous trans- 

 verse muscular septa, which suspend the 

 alimentary canal. Head separated by a 

 slight constriction, somewhat narrower than 

 the body, and triangular (when viewed from 

 above), the apex forwards ; eyes none ; body 

 fm-nished with two kinds of bristles, mostly 

 in tolerably equidistant groups, and these 

 in four rows, but their arrangement is 

 not constant ; two upper or dorsal rows of 

 setae longest towards the head, rather longer 

 than the width of body, consisting usually 

 of three to five long setaceous, and two 

 short bifid bristles, the two ventral groups 

 with three short bifid bristles ; towards the 

 posterior end of the body the bristles become 

 shorter, the setaceous ones absent, and near 

 the end the groups are represented each by 

 one short bifid bristle. Blood red. Poste- 

 rior end of body rounded ; anus terminal. 



This animal lives in mud, and when un- 

 disturbed, protrudes about one-third of the 

 anterior part of the body from the mud into 

 the supernatant water, where it exercises a 

 constant undulatory and to-and-fro motion. 

 When in numbers, they give the surface of 

 the mud a blood-red appearance, and if dis- 

 turbed, instantly retract entirely into the 

 mud. They sometimes crawl upon water- 

 plants, Confervse, &c. Their length is very 

 variable; from 1-5 to 3-4", or even more. 



They are transparent, and show well the 

 alimentary canal, with its peristaltic actions, 

 and the cilia lining it; the blood-vessels 

 and their movements, with the loops bathed 

 in the chylaqueous liquid, and the coiled 

 water- (respiratory or renal) vessels with 

 their cilia. 



BiBL. Schmidt, Miiller's Archiv, 1846. 

 p. 406 ; Duges, Ann. d. Sc. nat. 2 ser. xv. 

 p. 319; Johnston, Catal. of British Non- 

 parasitical Wortns. 



NAILS. — These organs, which consist of 

 modified epidermic formations, are imbedded 

 posteriorly and laterally in depressions, or 

 are covered at these parts by a fold of the 

 skin. The posterior depression (fig. 509 d) 

 is much deeper than the lateral depressions 

 (fi^ 510 c). 



The nail itself consists of the root (fig. 

 509 I), the body (k), and the free end (m). 

 The root extends over that part of the matrix 



2 g2 



