OF THE DESMIDIE^. 



(Mr. Balfs says) can any portion of the contents of the cell be forced out from 

 the extremities." More recently the belief in terminal apertures has been 

 revived by the published researches of the Kev. Mr. Osborne and others 

 (J. M. S.), who affii-m, that not only the outer hard case, but also the mem- 

 branous lining is penetrated by foramina, through which water enters from 

 without into the ca\-ity of the frond. Another writer in the Mic. Journ., Dr. 

 "Wright, describes, in a specimen of CJosterium didymotieum, certain circular 

 markings, consisting of two concentric ring-s, as apertui^es penetrating " both 

 layei-s of the investing membrane at irregular intervals:" yet neither the 

 character of these circular bodies, as represented by their observer, nor their 

 irregular distribution, countenances such a notion, and the appeal he makes 

 to Mr. Ealfs's figures, instead of aiding his argument, is totally subversive of 

 it ; for although, in the fronds of Closterium didymotieum and of C. Balfsiij 

 some large globules are distinguishable, these are in single linear series in a 

 definite and constant position, except when disturbed from it by the death of 

 the plant, or by its exhaustion by parasitic growths upon it, and clearly are 

 not aperiui'es. Besides, any such globules are sought in vain when the frond 

 is empty, as Mr. Ralfs distinctly shows by his figiures ; whereas if they were 

 openings, they would then be more evident than when the fnistule is filled 

 with its endochrome, Mr. Wenham {J. M. S. 1856, p. 159) has been un- 

 able to confiim the presence of apertiu'es, and writes — " It may be assumed 

 that if such an opening existed it would have something like a structui'al 

 margin of such a size as to allow its position at least to be visible under the 

 microscope, but not the slightest break can be observed in the laminated 

 structui-e that the thickened ends display." 



MovEME]!f TS AJfD EXTERNAL CiLiA. — By coutiuued observation the Desmidieai 

 are seen to move very slowly onwards, or with an oscillating movement 

 backwards and forwards. This phenomenon is most notable in the long 

 spindle-shaped fronds of the genus Closterium ; in others it is scarcely, in 

 many not at all, cognizable. Ehrenberg having persuaded himself of the 

 existence of pedal organs or papillae at the extremities of the fronds of Clos- 

 terium, found no difficulty in explaining their locomotion; but other observei^, 

 who deny the presence of such organs, have been compelled to seek some 

 other explanation of the subject. Some have referred the locomotion to the 

 influence of the vital acts taking place within the organism, to the extri- 

 cation of gas, &c. ; others again, particularly of late, have attributed it to 

 the presence of cilia covering the suiface. This latter hypothesis is sup- 

 ported chiefly by the Rev. Mr. Osborne and Mr. Jabez Hogg, who represent 

 these organs as covering the fronds of Closteymmi, of Staurastruin, and of 

 other Desmidieae (see page 7, on the Circulation). Mr. Wenham has 

 sought cilia in vain, and attributes the supposition of their existence to an 

 optical illusion. Powerful oblique sunlight, which is found necessary to 

 display the apparent ciliary movement, this obseirver remarks, " causes a 

 refractive atom to appear elongated as a ray or line . . . . , and this line also 

 to appear to extend over the boimdary of a cell- wall or other a^oining body: 

 another cause of deception arises from a large angle of aperture." The pos- 

 sibility of such errors he illustrates by reference to the circulation as seen 

 in Anacharis. In those fronds invested with a mucous sheath, cilia on the 

 surface of the lorica could perform no locomotive function, and therefore can 

 scarcely be supposed present. Likewise in the concatenated species they 

 cannot be looked for, since any movements they possess are of that general 

 sort seen in other filiform Algae, springing from vital action under the 

 influence of light. 



Apart from this inconsiderable movement, seen under the microscope, the 



