262 On Oceanic Infusoria, Liviny and Fossil. 



the vegetable side, especially since the brilliant discoveries of Mr 

 Thwaites,* communicated to a late meeting of the British Associa- 

 tion, have shewn that their fructification is precisely analogous to 

 that of some of the lower algse, and that the fruit resembles a spore. 

 A similar mode of fruiting is now discovered among Desmidiese, 

 which were also classed with infusoria by Ehrenberg, and, of these, 

 a large number, in fruit, are figured in the work of Mr Ralfs, before 

 alluded to ; but, as they are natives of fresh water, it is out of place 

 to enter on their history here. I may, however, remark, that the 

 curious spiny bodies found fossilized in flint, which often pass for 

 Xanthidia, are now proved to be only the spores of various genera of 

 DesmidiecE, whose full-grown fronds are amazingly unlike the spore 

 in form. The mode of forming fruit in both these families, Desmi- 

 diecd and DiatomacecB, which is also the mode among undoubted algse, 

 is by the coupling together of two cells or frustules, when a j>assage 

 is gradually formed between them, through which the contents of one 

 cell are discharged into the other, where a dense mass of granular 

 matter collects, which, at length, solidifies into a spore, and bursts 

 through the walls of the cell. As such a process of reproduction is 

 more analogous to what takes place in the vegetable than in the ani- 

 mal kingdom, naturalists seem now generally agreed to class them 

 with vegetables. The advocates for their animal nature appeal to 

 certain motions, having the character of voluntary motion, observed 

 in many species. Thus, Bacillaria paradoxa alternately propels its 

 frustules forward, and draws them back, opening out the filament of 

 which the compound body consists into a straight line, and contract- 

 ing it again into a narrow compass. This little plant resembles a 

 pack of narrow cards, joined together at one of the angles of their 

 smaller end ; when extended, they are ranged in a straight line, and 

 when contracted, they are folded back on each oiher, and lie as if in 

 a pack. It is highly curious to watch the regular manner in which 

 this motion is continued. Some of the other species have movements 

 of a similar character, but many have not been observed in motion ; 

 and such motions as are seen, more resemble the regulated movement 

 of a machine than the voluntary changes of place which animals ex- 

 hibit. No doubt it is difticult, peihaps impossible, to draw a rigid 

 line between the irritability of a vegetable and the muscular and ner- 

 vous contractions of an animal, when we come to investigate such 

 minute organisms as those we are now considering ; but it is, at 

 least, cei'tain that mere motion, such as has been observed in the 

 Diatomacese, is no proof of animality. And as the other points in 

 their history ally them to the vegetable kingdom, the fact of their 

 vegetability, if not quite proved (as I believe it to be), is, at least, 

 extremely probable. 



See Thwaites, in " An. Nat. Hist.," N. S., vol. 1., p. 162, &c. 



