I'iO Mr. 11. J. Carter on the Orgnnizittion of Infusoria. 



now uiutstraiiu'd by the tlia|)liaiu' and oflicr soft parts, cause 

 dchiscciu-c, and the ovules are set at Hberty (I'l. VI. lig. (K)). May 

 wc not iuier that the siht'c<)U.s IVustule of Navicida is siniihirly 

 situated to this tibrous layer, and that it also derives its power of 

 motion from an external eoating of diajjhane? That there is a gela- 

 tinous layer external to the frustule probably in all J)i(it()me<e, may 

 fretjuently be seen, althongh it may not be always endowed with 

 nmbility. In a speeies of l*a/mt'//cfi too, like (il(i'(>ca//s-fi granosa, 

 Kg.*, whieh I have had under observation, the transparent ex- 

 ternal covering ("envelope-cell " of Cohn) not only at one period 

 presents an aetinophorous form, but also mov(!s about under 

 this condition, bearing the green elliptical cell within (singly, or 

 divided into two or four, &c. as the case may be), whose form 

 ilcpends ujjon the presence of a more or less lirm (skeleton) coat, 

 that corresponds in position and oHice to the spiral coat in 

 Eiiglena and the siliceous frustule in Nariculu, viz. in supporting 

 the contents of the sarcode and chlorophyll-bearing protoplasm, 

 and in sustaining th(;ir form in all these organisms respectively 

 (tig. ID). In (Jscillaloria {jjrinccjis, Kg., mihi) again, although, 

 like Nuricu/ii, the {jreseiice of a layer of substance endowed with 

 motion round the cells cannot be seen, yet, when we observe 

 the whole ehain of a fragment moving slowly backwards and for- 

 wards within its sheath, and even extending beyond it, so as to 

 force out the loosened cells at either end (probably for the 

 formation of new filaments), wc can con)c to no other conclu- 

 sion, that I see, than that each cell, which corresponds in office 

 to the frustule in Nnvicula, &c., is surrounded by a transj)arent, 

 gelatinous substance, endowed with motion, and that, cii masse, 

 they perform this act : although this substance cannot be seen 

 when the cells are undergoing simple elongation or filamentous 

 development, yet it becomes evident enough when they are 

 undergoing crucial division without the sheath for the multi- 

 plication of filaments. In none of these instances does this 

 envelope, if existing in Navicida, as well as the rest, present any 

 change on the addition of iodine but a yellow tinge, even when 

 assisted by sulpliurie acid ; and it th(;refore apj)cars to be entitled 

 just as much to the term of diaphane in Navicu/a (if present), 

 (Jlreocajjsa (jranosa ((), and Oscil/aluria, as in the Infusoria. In 

 Closlc/iuin there are no signs of an organ of this kind externally, 

 exwpt at the extremities, where it may be an extruded part of 

 the ciliated protoplasm within; for C. liatula, an Morren has 

 stated, can fix itself by one end, and ])artially rotate upon that 

 end ; while in Spiroyijra this much extrusion of the protoplasm 



* HtenuitticuiCHS r/ranosus, Ilasaall, jil. 81, i\^. (>, IJntisii Freshwater 

 Alga:; — but with cells scattered, not continuous. 



