DIATOMACE^!. 417 



not so the Diatomacem, which offer many interesting struc- 

 tural characteristics of sufficient importance to warrant our 

 keeping them in the animal division. They are most 

 striking objects under the microscope, from the very pecu- 

 liar beauty and variety of their forms, and from their 

 bilateral symmetry, external markings, and indestructible 

 siliceous skeletons ; so that we believe they would be more 

 correctly placed in a median, or Molluscian sub-kingdom. 

 Appearing everywhere with the first-born of life, and 

 wherever matter is found in a condition fit for their deve- 

 lopment and nourishment, these marvellous indestructible 

 creatures have been preserved and brought down to us, in 

 forms unchanged, from the remotest periods of our globe's 

 history; and supplying, as they do to the microscopist, 

 some of the most valuable test-objects, the Gyrosigma, 

 Grrammatophora, Fragilaria, fiipidopJiora, Pleurosigma 

 angulatum, with many others, it cannot be a matter of 

 surprise that considerable attention should have been di- 

 rected to them, and an earnest inquiry instituted into their 

 nature and structure. 



"Comparing," says Kiitzing, "the arguments which 

 seem to indicate the vegetable nature of Diatomacece with 

 those which favour their animal nature, we are of ne.ces- 

 sity led to the latter opinion. If we suppose them to be 

 plants, we must admit every frustule, every Navicula to be 

 a cell. We must suppose this cell with walls penetrated 

 by silica, developed within another cell of a different 

 nature, at least in every case where there is a distinct 

 peduncle, or investing tube. In this siliceous wall we 

 must recognise a complication certainly unequalled in the 

 vegetable kingdom. It would still remain to be proved 

 that the eminently nitrogenous internal substance corre- 

 sponded with the generic substance, and that the oil 

 globules could take the place of starch. The multipli- 

 cation would be a simple cellular reduplication ; but it 

 would remain to be proved that it takes place, as in other 

 vegetable cells, either by the formation of two distinct 

 primitive utricles, or by the introflection or constriction of 

 the wall itself. Finally, there would still remain un- 

 explained the external motions and the internal changes ; 

 and we must prove the accumulated observations on the 

 E E 



