INTRODUCTION. 21 



any doubt of its truth, and although I have myself failed to 

 perceive their actual movement, I have sufficient evidence 

 of its occurrence. But, whilst making this admission, I must 

 still maintain that in the lower tribes of organic life motion 

 is not an indubitable sign of an animal nature*, and that 

 the movements of the Desmidiese must be very sluggish, or 

 exercised only under peculiar circumstances, since T have 

 never witnessed it, notwithstanding I have almost daily living 

 specimens under my inspection. Mr. Jenner has been 

 equally unsuccessful, and several friends, experienced in the 

 use of the microscope, either have not seen it or speak of it 

 in uncertain terms f. 



Professor Bailey states that " their power of locomotion 



* " Motum non determinare limites regni animalis exinde patet, quod sunt 

 animalia, quae non moventur, vegetabilia in quibus motum vividum videmus." 

 Agardh, Conspectus Diatomacearum, p. 4. 



" The active motions in plants and their parts, especially in Algae, ought 

 not to give rise to the supposition of an animal nature, even when they 

 are called infusorial or animal motions." — Ehrenberg, Taylor's Scient. 

 Mem. vol. i. p, 5S6. 



t I subjoin the opinions of various observers : — 



" Actual motion, arising from internal causes, I saw only in Sphserastrum ; 

 and the slight movement, supposed to have been observed in some of the 

 genera, is certainly of the same description as that of some Confervse." — 

 Meyen, 1839, as quoted in Pritchard's Infusoria, p. 180. 



" These are animals instead of plants, if the faculty of locomotion w^ill 

 entitle them to that rank." — Carmichael, in Hook. Br. Fl. vol. ii. p. 398. 



" It was impossible to determine whether the vague motions of Closterium 

 were voluntary or not." — Dalrymple, see Annals of Nat. Hist. vol. v. p. 417. 



*' Motions apparently voluntary are easily seen .... I have seen Euastrum 

 margaritiferum move quite distinctly." — Bailey, American Bacillaria. 



" EUes n'ont pas un mouvement sensible sur le porte objet du microscope. 

 Cependant il est facile de remarquer dans les localites ou elles vivent ovi dans 

 les vases ou on les conserve, qu'elles se dirigent vers la lumiere et se rapprochent 

 en pellicules oii en sortes de pinceaux d'un beau vert, reunies entre elles au 

 moyen d'un mucus qui les entoure ordinairement." — Brebisson, in Chevalier's 

 ' Des microscopes et leur usage.' 



" The various species of Closterium, as well as the closely allied Euastra. 

 have a distinct motion which cannot be referred to any extrication of gas. 

 I have had species of Closterium and Euastrum confined in a compressor, in 

 •water perfectly free from other bodies, and they moved so fast that I found 

 it impossible to sketch their forms by the camera lucida until they were 

 killed." — Professor Bailey in lit. 



