OF THE DIATOME.E. &3 



other. And," he continues, '' I rely upon the observation that there is some 

 motion and successive alteration in them, as if these minute globules mixed 

 with larger ones, and separated again from them." For, to the mind of 

 the Italian naturalist, the hypothesis of stomachs is admissible, although 

 the fact that a polygastric structure (affirmed by Ehrenberg) has not been 

 shown in the ciliated Protozoa is in itself an a priori argument that such an 

 organization is not to be found in the Diatomeae, among which animal cha- 

 racteristics are so much more deficient and indeterminate. 



Although, to our apprehension, this argument, based on the diiferential 

 chemical composition, to the extent it is developed by Meneghini, is incom- 

 plete and inconclusive, yet it was a duty to present it, in order that some of 

 the many ardent English microscopists may be induced to attempt the solution 

 of this micro-chemical question. 



Rabenhorst, we should not omit to state, describes the colouring matter of 

 Diatomca? as quite different from the chlorophyll of plants. For instance, he 

 states that the chlorophyll of plants is taken up by alcohol, dissolves with a 

 yellowdsh-green colour in alkalies, and with muriatic acid acquii'es an emerald- 

 green colour, whereas the coloming material of Diatomece is insoluble in 

 alcohol (although after a time its coloiu" fades), remains unchanged by alkalies, 

 and acquires a pale-green colour mth muriatic acid. 



It still remains to point out the facts which speak in favom' of the vegetable 

 nature of the Diatomacese. The following summary was offered by Kiitzing : — 



" 1. The great resemblance of compound forms to xilgse, and their develop- 

 ment by fission. There are, indeed, compound Infusoria, as Monad-masses 

 and Polypes : but the former are very questionable animals ; and the latter 

 have this essential distinction, that the individual animal lives without 

 (external to) its habitation, and moves freely, whereas such Naviculce as 

 Encyonema, Scliizonema, and Micromega, and similar genera, grow within the 

 enclosing substance, building themselves up like the cells in the stem of a 

 plant — so vegetating here only as cells. In like manner, the individuals of 

 Fragilaria, Melosira, Himantidium, &c., are steadily fixed, and unable to 

 exhibit animal motion. 



"2. The inner soft organic parts, which I have designated gonimic sub- 

 stance, possess, as well in their chemical nature as in theii' development, 

 peculiarities akin to those met T\dth in the ceU- contents of confervoid Alg^e. 



*' This relation is most clearly seen in the genus Melosira and its allied forms, 

 which, not only in form, but also in the chemical components of their con- 

 tained matter (since the presence of chlorophyll is common to all Diatomea?), 

 are closely allied to the confervoid Algae. 



" 3. The development of seeds, or young [as Kiitzing represents it], occurs 

 here as in undoubted Algae, but never as in true animals. 



" 4. The Diatomeae, and especially the free moving Naviculce, develope, in 

 the sun's rays, an appreciable quantity of oxygen, like all admitted plants. 



" The evolution of oxygen, indeed, occurs in green Monads and Euglence ; 

 but this affords no argument for the animality of the Diatomeae, but renders 

 the animal nature of those Infasoria themselves veiy doubtfirl, and the more 

 so as recent observations confirm the idea of the origin of the lower plants 

 themselves from Monads and Euglence. AVherefore all these comparisons 

 serve to favour the belief in the vegetable nature of Diatomeae." 



To these arguments has been added another, resting on the assumption of 

 conjugation being peculiar to plants ; and Mr. Blackwell chscovers further 

 evidence of plant-life in the variations of form of the fmstules of the same 

 species (J. M. S. 1853, i. p. 247). 



It is necessary to inquire, seriatim, into the real value of the arguments 



