CHONDRIA. 



[ 140 ] 



CHORDA DORSALIS. 



(the common Dory). The body is covered 

 with short reflexed spines. Length 4-5". 

 BiBL. Baird, Brit. Entomostr, p. 327. 

 CHONDRIA, Ag. See Laurencia. 

 CHONDRINE.— The gelatinous matter 

 of the permanent true cartilages. 



Its solution differs fi'om that of the gelatine 

 of bones, &c., in being precipitated by acetic 

 acid, acetate of lead, and alum. The acetic 

 precipitate is insoluble in excess. 



It is coloured red by Millon's test ; but is 

 unaffected by that of Pettenkofer. 

 BiBL. See Chemistry, Animal. 

 CHONDRUS, L.— A genus of Cryptone- 

 miaceae (Florideous Alga;), composed of car- 

 tilaginous sea-weeds with flat, dichotomously- 

 divided fronds, the cellular structure of which 

 exhibits three layers ; a central of longitu- 

 dinal filaments, an intermediate of small 

 roundish cells, and an outer of vertical, 

 coloured and beaded rows of cells, the whole 

 imbedded in a tough " intercellular " matrix. 

 See Intercellular substance. 



Fructification : spores contained in favel- 

 lidia immersed in the frond ; tetraspores 

 collected in imbedded sori,and "nemathecia," 

 tubercles composed of radiating filaments 

 (antheridia?). C. crispus becomes horny 

 when dry, and is the Irish moss or Carrigeen 

 of the shops. 



BiBL. Harvey, Br. Mar. Alg. pi. 17 D.; 

 Phyc. Brit. pi. 63 & 187 ; Greville, Alg. 

 Brit. pi. 15. 



CHORDA, Stackh. — A genus of Lamina- 

 riaceae (Fucoid Algae), with fronds of a pecu- 

 liar, simple, cylindrical form ; two species, 

 C.filum and C. lomentaria, are found between 

 tide-marks on British coasts ; the former 

 grows from 1 to 20 or even 40 feet long, with 

 a greatest diameter at half its length of 1-4" 

 to 1-2". The cord-like frond is tubular, but 

 has at intervals thin diaphragms, formed by 

 interwoven transparent filaments. The wall 

 of the tube is composed of a number of layers 

 of very regular six-sided cells^ upon which 

 are implanted little erect clavate cells which 

 coat the entire surface of the fi'ond. These 

 present two forms, apparently constituting 

 oosporanges{spores,}lsiVwey,2)aranemata,Ag.) 

 and trichosporanges {antheridia, Harvey, 

 spores, Ag.). The first are single sacs pro- 

 ducing a number of zoospores, the second 

 are filaments composed of about five joints, 

 each of which give birth to a zoospore. 



BiBL. Harvey, Br. Mar. Alg. 31. pi. 3 B. ; 

 Phyc. Brit. p. 107, &c. ; Thm'et, Ann. des 

 Sc. nat. 3 ser. xiv. p. 240. pi. 29. figs. 5-10 ; 

 Derbes and Solier, Ann. des Sc. nat. 



3 ser. xiv. 268. pi. 33. figs. 7-10; Kiitzing, 

 Phyc. generalis, pis. 28 & 29. 



CHORDA DORSALIS.— The embryonic 

 representative of the spinal column of the 

 Vertebrata ; the permanent spinal column of 

 the Cartilaginous Fishes. It sometimes forms 

 a spindle-shaped, transparent, gelatinous- 

 looking cord, with the broadest part near 

 the tail; at others it is cylindrical or conical, 

 rounded anteriorly and tapering posteriorly. 



It usually consists of an outer compara- 

 tively thick and firm structureless membrane, 

 forming a sheath, and of pale nucleated cells, 

 which fill the sheath (fig. 130). In some 



Fig. 130. 



Magnified 350 diameters. 



Portion of the chorda dorsalis of the embryo of a sheep, 

 rather more than 1-2" in length, a, sheath ; b, cells. 



instances, however, its structure is fibrous, 

 and that of the sheath fibro-membranous. 

 The cells are mostly angular or polyhedral, 

 and closely crowded. Their size varies ; in 

 the embryo of a sheep rather more than 1-2" 

 in length, they measured about 1-1800". 



The walls of the cells readily dissolve in solu- 

 tion of potash; but they yield neither gelatine 

 nor chondrine on boiling. The liquid within 

 the cells is not coagulated by boiling, but 

 the chorda itself becomes cloudy and granular. 



In its earliest stage of development, the 

 chorda consists simply of alongitudinalband of 

 ordinary formative or embryonic cells ; the 

 sheath is subsequently formed. It appears that 

 the spinal column is not developed from the 

 chorda itself, but from a blastema secreted 

 by its component cells and effused around 

 them. 



The chorda is most readily examined in 

 the larvae of frogs (tadpoles), of Tritons, or of 

 Fishes ; and may be separated by macerating 

 the dead animals for twenty- four hours in 



