28 INTRODUCTION. 



chrome has escaped with considerable force. This is espe- 

 cially the case with Closterium Lunula ; and the same circum- 

 stance occurs in most of the Desmidieae, although in none of 

 the others so remarkably as in that genus. Mr. P. Grant 

 has favoured me with an account of numerous experiments 

 which he instituted to determine the effects of different sub- 

 stances on the Desmidieae, Conjugatse, &c. From these it 

 seems that the action of a reagent cannot be predicated with 

 any certainty, and that the molecular motion is not affected 

 by several strong poisons, whilst it yields to other substances 

 less generally deleterious. 



With regard to the " supposed ova," I fully agree with 

 Meyen that " they are similar to the green corpuscles found 

 in the cells of the Confervse," and, when both are removed 

 from their cells, I am persuaded that it would be impossible 

 to distinguish between them. That they contain amylum 

 has been, with good reason, pointed out by Meyen as decisive 

 against the notion that they are eggs. 



The latest advocate of the animal nature of the Desmidiese 

 is C. Eckhard, in his memoir ' on the Organization of the 

 Polygastric Infusoria,' published in Weigmann's Archiv, part 

 3, 1846. With this memoir I am acquainted only through 

 the medium of a translation by Dr. J. W. Griffiths in the 

 * Annals of Natural History*.' It is apparently written for 

 the purpose of confirming Ehrenberg's views, and accordingly 

 defends his accuracy in every respect. So far as regards the 

 Desmidieae, Eckhard notices only the Closteria, and he ad- 

 vances nothing additional except an opinion that the trans- 

 verse suture is a fissure or mouth. In order that both sides 

 of the question may be compared, I extract his remarks, and 

 merely point out that he has left unnoticed the facts on which 

 botanists place their chief reliance : — 



" The grounds for their being of animal nature are derived 

 partly from their motion, partly from their organization. 

 On the leaves of Ceratophyllum, I observed the manner in 



* Vol. xviii. p. 433. 



