278 THE MICROSCOPE. 



Desmidiacece. — A remarkably beautiful family of confer- 

 void algae, the most distinctive characteristics of the species 

 being their bilateral symmetry. Each frustule is, however, 

 a perfect unicellular plant, with a homogeneous structureless 

 membrane, enclosing a cellular skeleton filled with chloro- 

 phyll. Four modes of reproduction have been observed in 

 the desmids, and many points still remain to be cleared 

 up. Braun remarks of the products of conjugation, *' that 

 they do not pass, like the swarming-cells of the Palmellacew 

 and the reproductive cells of the Diatomacese, directly and 

 by uninterrupted growth into the primary generation of 

 the new vegetative series, but persist for a long time in a 

 condition of rest, during which, excej^ting as regards im- 

 perceptible internal processes, they remain wholly un- 

 changed. To distinguish these from the germ-cell (gonidia) 

 I shall call them seed-cells (spores). Certain early condi- 

 tions observed in Closterium and Uuastrum, namely, families 

 of unusually small individuals, enclosed in transparent, 

 colourless vesicles, render it even probable that in certain 

 genera of this family a number of individuals are produced 

 from one spore, by a formation of transitory generations 

 occurring already within the spore." ^ 



contractile, even locomotive power, need not on this latter account be assumed 

 as therefore necessarily an animal. In the former category fall the Volvocinaccpe 

 and Rhisidium ; in the latter category Englena and its allies, the so-called 

 Astasisean Infusoria, suggest themselves; and these must of course wait until 

 their reproduction and history are better known befoie Ave can feel satisfied as 

 to their true position ; yet it seems highly probable that these wiU presently, if 

 they do not even now, take their place amongst admitted plants. 



"Several writers have, indeed, from time to time, put forward th& (now, I 

 think, generally accepted) view that the protoplasm of the vegatable and the 

 sarcode of the animal cell are identical in nature ; and, in seeking for analogies 

 as regards contractility in the vegetable protoplasm as compared Avith the 

 animal, and as demonstrative thereof, special attentit)n has been directed to 

 several of the now familiar phenomena displayed by certain vegetable cells. 

 Such are the vibratory movements of ciliie, and drawing in of these, the circula- 

 tory movements of the cell contents, as in the hairs of theTradescantia, &c., the 

 contractile vacuole in Gonium, Volvox, Ac, ;md so forth. But while these are, 

 I think, unquestionably to a considerable, but more limited extent, manifesta- 

 tions of the same phenomenon, it seems to me that none of these cases present 

 so exact an analogy, strongly as they may indicate it, with the rhizopodous con- 

 tractility as do the amo'boid bodies of Stephanospluera, of Volvox, of the 

 Moss-radicles, and of Rhisidium. The amoeboid bodies of Stephanospluera seem 

 to disjilay this rhizopodous contractility in greatly the most marked or ex- 

 aggerated degree, as their vigorous and energetic power of locomotion indicate : 

 in them, and indeed in those of Volvox, the Moss, and Rhisidium, the pseudo- 

 podal processes and their mode of protrusion and withdrawal, the flow of the 

 granules, and the locomotion of the whole body, were in all resxiects analogous 

 to the similar phenomena evinced by a true ama?.ba." — Wm. Archer, Quarterly 

 Journ. Micros. Science, vol. v. p. ISri. 



(1) " The Phenomenon of Rejuvenescence in Nature." 



