Insects. 1231 



It is, however, difficult to say what is an incontrovertible fact in nature, till naturalists 

 can be said to he perfectly acquainted with all the habits and economy of every animal 

 that falls under their observation ; and to this degree of knowledge no one, I suppose, 

 will be bold enough to lay claim. 



Another instance of an animal feeding on a mineral substance has occurred to my 

 mind, since writing my former letter; and as it appears in some measure confirmatory 

 of the fact therein related, I beg to mention it, in the hope that some discussion on the 

 subject may be elicited in the pages of your interesting periodical. 



The rank or position which the sponges occupy in the scale of nature is, it is true, 

 still a matter of dispute ; for while many distinguished naturalists contend for their 

 animal organization, others equally eminent affirm, that they differ in no essential 

 character from vegetables. Those, however, who consider them to be of an animal 

 nature, — although zoophytes and occupying the lowest form of animal life, — will 

 hardly be able to deny, that that life is supported, at least in a very great degree by 

 mineral substance, as neither the vegetable nor animal kingdom appears to furnish any 

 part of its subsistence. " Nothing more seems necessary to their sustenance and 

 growth" (says Dr. George Johnston in his ' History of British Sponges ') " than the 

 admittance of the circumfluent water, since like plants, they appear to live solely on 

 water and its mineral ingredients." 



No great stress can indeed be laid upon this instance, from the nature of the being 

 whose mode of subsistence is here adduced]; all those who do not admit its animaliza- 

 tion, will of course consider the argument as of no force. 



A circumstance, however which fell under the notice of an eminent naturalist more 

 than twenty years ago, and with which I very recently became acquainted, will be con- 

 sidered worthy of attention. 



There is a letter in the 61st volume of the * Philosophical Magazine and Journal ' 

 entitled ' On animals receiving their nutriment from mineral substance ; by the Rev. 

 W. Kirby, M.A., F.R.S., F.L.S.' I do not find that this letter attracted much obser- 

 vation at the time, at least I see no mention of it in other volumes to which I 

 have access ; and as the work may not be of easy reference to all, I beg to enclose a 

 copy of Mr. Kirby's communication. 



Barham, January 16th, 1823. 

 " To the Editor of ' The Philosophical Magazine and Journal.' 

 " Gentlemen, — Mirbel has proposed to distinguish vegetables from animals by the 

 different nature of their food ; the former deriving their nutriment, as he affirms, from 

 inorganic matter, and the latter from organic. Another able and learned physiologist, 

 Dr. Virey, in the ' Nouveau Dictionnaire d' Histoire Naturelle,' article, ' Aliment ', 

 maintains on the contrary, that plants as well as animals, are supported by organic 

 food ; since as he contends, it is the debris of organized matter, mixed with the soil, 

 that furnishes plants with their appropriate pabulum, as likewise those animals, such 

 as earth-worms, the larvae of ephemerae, &c. which have been supposed to live upon 

 earth. He also excludes water and air from the functions in question. The argu- 

 ments which he adduces in support of his hypothesis appear ingenious and forcible : 

 the principle one is that the fertility of a soil depends upon the quantity of humus or 

 vegetable earth that it contains ; and that worms, &c. are not to be found in very bar- 

 ren soil. Still, however, there is no general rule without some exceptions : and one 

 has fallen under my own notice, which seems to prove that there are animals that can 

 derive nutriment from mineral substance, in which there is no debris of organized mat- 



