120 Mr. HvJ. Carter on the Organization of Infusoria, 



now unrestrained by the diaphane and otlicr soft parts, cause 

 dehiscence, and the ovules are set at liberty (PI. VI. fig. 60). May 

 we not infer that the siliceous frustule of Navicuia is similarly 

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

 motion from an external coating of diaphane? That there is a gela- 

 tinous layer external to the frustule probably in all Diatomece, may 

 frequently be seen, although it may not be always endowed with 

 mobility. In a species of Palmellea too, like GloBocapsa granosa, 

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

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

 presents an actinophorous form, but also moves about under 

 this coiulition, bearing the green eUiptical cell within (singly, or 

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

 depends upon the presence of a more or less firm (skeleton) coat, 

 that corresponds in position and office to the spiral coat in 

 Euglena and the siliceous frustule in Navicuia, viz. in supporting 

 the contents of the sarcode and chlorophyll- bearing protoplasm, 

 and in sustaining their form in all these organisms respectively 

 (Hg. 19). In Oscillatoria (princeps, Kg., raihi) again, although, 

 like Navicuia, the presence of a layer of substance endowed with 

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

 the whole chain 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), we can come to no other conclu- 

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

 to the frustule in Navicuia, &c., is surrounded by a transparent, 

 gelatinous substance, endowed with motion, and that, en 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 Navicuia, as well as the rest, present any 

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

 assisted by sulphuric acid ; and it therefore appears to be entitled 

 just as much to the term of diaphane in Navicuia (if present), 

 Gloeocapsa granosa (?), and Oscillatoria, as in the Infusoria. In 

 Closterium there are no signs of an organ of this kind externally, 

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

 the ciliated protoplasm within ; for C. lunula, as Morren has 

 stated, can fix itself by one end, and partially rotate upon that 

 eud J while in Spirogyra this much extrusion of the protoplasm 



* Hamatococcus granosus, Hassall, pi. 81, fig. 6, British Freshwater 

 Algae i— but with cells scattered, not continuous. 



