26 INTRODUCTION. 



approaching to a satisfactory proof of his position can be 

 deduced. In offering these remarks I hope I shall not be 

 suspected of the least wish to undervalue Ehrenberg'sdis- 

 coveries. I believe that he is sometimes too hasty in arriving 

 at his conclusions, and that his knowledge of the Desmidiese 

 is less accurate than of the Diatoraacese and other tribes 

 which have come under his observation. When we consider 

 the extent of his researches, it is not surprising, eminent as 

 he is, that he should fall into some errors, which a person 

 inferior in ability, but confining his whole attention to a 

 comparatively smaller range, is likely to detect. Nor even 

 in respect of this family, although I must consider it the 

 most defective portion of his great work, are the obligations 

 slight which we owe to Ehrenberg : for not only has he 

 enlarged our knowledge of the Desmidiese by the discovery 

 of many new facts, by his discrimination of the species, and 

 by producing better representations than those which pre- 

 viously existed, but he has given an impulse to the study, 

 and rendered it popular. 



The fifth volume of the 'Annals of Natural History*' 

 contains an abstract of a paper by Mr. Dalrymple on the 

 Closteria, read before the Microscopical Society of London, 

 from which I quote the following reasons for placing them in 

 the animal kingdom : — 



" 1st. That while Closterium has a circulation of mole- 

 cules greatly resembling that of plants, it has also a definite 

 organ, unknown in the vegetable world, in which the active 

 molecules appear to enjoy an independent motion, and the 

 parietes of which appear capable of contracting upon its 

 contents. 



"2nd. That the green gelatinous body is contained in a 

 membranous envelope, which, while it is elastic, contracts 

 also upon the action of certain reagents whose effects cannot 

 be considered purely chemical. 



" 3rd. The comparison of the supposed ova with cytoblasts 



* P. 415. 



