SPIROCHJETA. 



[ 715 ] 



SPIROGYRA. 



1-120,000". Perty describes a red and a 

 black variety. 



S. volutam (PI. 7. fig. 23). Filaments 

 very tortuous, distinctly jointed, with a 

 cilium at each end ; spiral of three, four, or 

 more turns; length 1-1400"; diam. 1-14,000". 



S. plicatik (Spirochceta plicatilis, Ehr.) 

 (PL 7. fig. 22). Filament very long, flexible ; 

 coils numerous ; movement undulating ; 

 length 1-180" ; diam. 1-12,000". 



BIBL. Ehr. Inf. 84; Dujard. Inf. 223; 

 Rabenht, Aly. ii/72. 



SPIROCH^ETA, Ehr. 8. plicatilis = 

 Spirillum plicatilc. 



SPIROCHO'NA, Stein. A genus of 

 Peritrichous Infusoria, family Vorticellina. 



S. gemmipara (PL 32. fig. 35) is found 

 upon the branchial plates of Gammarus 

 pulexj where also its remarkable Acineta- 

 form (fig. 36) occurs. 



S. Scheutenii is met with upon the feathery 

 setae arising from the terminal joints of the 

 post-abdominal legs of Gammarus. 



S. tintinnabulwn, on 7V#on-larv86. 



BIBL. Stein, Inf. ; Clap, et Lachm. Inf. 

 132; Kent, Inf. 660. 



SPIRODIS'CUS, Ehr. Under the name 

 S. fulvus, Ehrenberg places among the In- 

 fusoria, in the family Vibrionia, a brownish 

 organism, consisting of a short discoidal or 

 much- flattened helical spiral, 1-1200" in 

 diameter, and found in Siberia. It exhi- 

 bited a slow movement. Ehrenberg's figure 

 greatly resembles that in PL 40. fig. 34 (the 

 upper two), without the cilia, and magnified 

 200 instead of 400 diameters. (Ehr. Infus. 



Fig. 668. 



>PIROGY'RA (Zygnema, Agardh in 

 part) (fig. 668). A genus of Zygneinacese 

 (Confervoid Algaa), 

 mostly very elegant, 

 and all very interest- 

 ing on account of their 

 structure and modes 

 of development. They 

 are green filaments, 

 floating unattached in 

 standing fresh water. 

 They consist of jointed 

 tubes that is, rows of 

 cylindrical cells, some- 

 times of considerable 

 size, in the interior of 

 which the green co- 

 lou~attS r is a,- S '^T 

 ranged in one or more mamenta conjugating, 

 spiral lines running Magnified 200 diameters, j 



round the walls, these 



spiral lines presenting bright points at inter- 

 vals along their course (PL 9. figs. 17, 26, 27). 

 The green lines consist of bands of proto- 

 plasm coloured by chlorophyll. The bright 

 points are in some stages composed of 

 globules of similar substance ; but generally 

 they are occupied by starch-granules im- 

 bedded in the protoplasm j smaller starch- 

 granules also occur at certain stages 

 throughout the green band. A remarkable 

 lenticular nucleus is also present, suspended 

 in the centre of the cell by threads of proto- 

 plasm running out to the primordial utricle 

 lying against the cell-wall. Sometimes this 

 nucleus is placed with its faces towards the 

 side wall (S. nitida, PI. 9. fig. 26) ; sometimes 

 it appears to be placed with its faces 

 looking up and down, as it presents the 

 appearance of a narrow ellipse when seen 

 sideways (S. pettucida, PI. 9. fig. 27). The 

 laminated structure of the cell-walls is also 

 curious, but will be better understood after 

 a sketch of the mode of development. 



The attractive appearance of the Spiro- 

 gyra and the easily observed phenomenon 

 of conjugation have caused much attention 

 to be paid to this genus ; and many points of 

 their history have been determined. The 

 cells composing the filaments all multiply 

 simultaneously when the plant is growing, 

 each becoming twice its length and divided 

 into two. It has been certainly observed by 

 Braun and Priugsheim that the division 

 is preceded by a division of the nucleus. 

 From this interstitial mode of growth it is 

 evident that the walls of the cells of plants 

 actively vegetating must soon become com- 

 posed of a number of layers belonging to di- 

 stinct generations of cells. Thus, supposing 

 we have an original cell , this encloses its 

 progeny, two cells 2 & b ; and when these 

 divide again and come to enclose respect- 

 ively a 3 & .c and b' 2 & d, the parent cell , 

 stretched to four times its original length, 

 still encloses the whole. The laminae be- 

 longing to the respective generations do not 

 become very intimately blended; for by ma- 

 ceration we may cause the outer membranes 

 to soften and dissolve, and set free the 

 younger cells intact. The older membranes 

 seem to have become thinner by stretching, 

 or by solution, midway between their septa, 

 since on maceration we may often see them 

 give way in the middle, and the young cells 

 slip out* from them, leaving them as short 

 hyaline tubes with a diaphragm in the mid- 

 dle. The ends of the cells of some species 

 present a curious appearance, which might 



