150 THE MICROSCOPE. 



Comparing the arguments which seem to indicate the vegetable 

 nature of Diatomaceee with those which favour their animal 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 in- 

 ternal substance corresponded with the genimic substance, and that the 

 oil globules could take the place of starch. The multiplication 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 unexplained the ex- 

 ternal motions and the internal changes ; and we must prove Ehren- 

 berg's observations on the exterior organs of motion to be false. But 

 again, admitting their animal nature, much would remain to be investi- 

 gated, both in their organic structure and their vital functions ; except- 

 ing this, so far as we know, we have only one difficulty to overcome, 

 that of the probably ternary non-azotised composition of the external 

 gelatinous substance of the peduncles and investing tubes. But as the 

 presence of nitrogen is not a positive character of animal nature, so the 

 absence of it is not a proof of vegetahk. And in order that the objec- 

 tion 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 Diatomacese were 

 proved by new and more circumstantial observations, this peculiarity, 

 if it deserve the name of objection, might still be regarded as an im- 

 portant discovery. 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. " I conclude," observes Kiitzing, 

 " however, that in the present state of science, the Diatomacese are 

 to be enumerated among animals." 



I should recommend microscopists to conduct their observations of 

 these and similar bodies in very shallow cells, say of from l-50th to 

 1-lOOth of an inch deep, covered with glass of from l-150th to l-250th 

 of an inch thick. The objective must be a l-4th or l-8th, with a 

 good eye-piece, and careful illumination — Eainey's moderator with a 

 Gillett's condenser or parabolic reflector. The examination should be 

 conducted during very bright weather, or sunlight. 



