338 



ALGJE FIGURATJI. 



FAM. XIX. DESMIDE.E. 



Char. Algae rarely filamentous, bipartite, of a ^figured out- 

 line, highly mucous. 



WE have arrived at length at the consideration of a most 

 ntercsting group and family of freshwater Alga, the essential 

 characteristics of which are the beautifully figured forms 

 and bipartite composition of the fronds of the numerous 

 species of which it is composed. 



The Desmidece have been the subject of considerable dis- 

 cussion respecting their animal or vegetable nature : the 

 question is now, however, all but settled in favour of their 

 vegetability. Amongst the advocates of their animal nature 

 may be mentioned the names of Ehrenberg and Mr. Dal- 

 ryrnple : the observations of the latter, however, were con- 

 fined almost exclusively to the genus Closterium. 



Ehrenberg rested the claims of the Desmidea to ani- 

 mality upon the mode of their increase by self-division, a 

 method of multiplication which it is now known belongs to 

 all the Algce, and which, therefore, cannot be allowed to have 

 any weight in the decision of the point in question. Mr. Dal- 

 rymple, however, in his memoir on the Closteria*, adduces 

 several\ther reasons for regarding them as animals, two only 

 of which apply at all to the other genera of Desmidea, the 

 remainder being alone applicable to Closterium : these are, 

 first, the fact that the inner delicate membrane, which lines 

 the outer symmetrical, and usually crescentic covering, con- 



See "Annals of Nat. Hist," vol. v. p. 415. 



