372 ANIMAL NATURE OF DIATOME^. 



nature we are of necessity 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 corresponded with the 

 gonimic substance, and that the oil globules could take 

 the place of starch. The multiplication would be a 

 simple cellular deduplication (sdoppiamento), 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 Ehrenberg's observations on the 

 exterior organs of motion to be false. But, again, ad- 

 mitting their animal nature, much would remain to be 

 investigated, both in their organic structure and their vital 

 functions; excepting this, so far as we know, we have 

 only one difficulty to overcome, that of the probably 

 ternary, non-azotised composition of the external gela- 

 tinous substance of the peduncles and investing tubes. 

 But as the presence of nitrogen is not a positive cha- 

 racter of animal nature, so the absence of it is not a 

 proof of vegetable. And in order that the objection should 

 really have some weight, it would be well to demonstrate 

 that this substance is isomeric with starch. For then, 

 supposing all the arguments in favour of the animal nature 

 of Diatomeae were proved by new and more circumstantial 

 observations, this peculiarity, if it deserve the name of 

 objection, might still be regarded as an important dis- 

 covery. We should then have in the animal, as well as 

 in the vegetable kingdom, a ternary substance similar to 

 that forming the basis of the vegetable tissue. 



