DISTINCTION BETWEEN ANIMALS AND PLANTS. 33 



to ~4raw the line in individual cases, it cannot be doubted that a boundary 

 <'x1st; and in general a very simple mark will suffice to establish the 

 distmchoiv. This mark is the presence or absence of a stomach or internal 

 cavitji/flh* the reception of food. The possession of a stomach cannot be 

 regarded, however, as in itself an essential distinction between the two king- 

 doms (as some have represented it) ; for its presence is merely a result, so to 

 speak, of tlje nature of the food of Animals, and of the mode in which it is 

 obtained. Vegetables are dependent for their support, upon those materials 

 only which they obtain from the surrounding elements ; carbonic acid, water, 

 and ammonia, duly supplied to them, with a small quantity of certain mineral 

 ingredients, afford all the conditions they require, for the production of the 

 most massive fabrics, and the greatest variety of secretions. But these same 

 elements, if supplied to Animals, could not be converted by them into the 

 materials of organized structures ; for they can only employ as food substances 

 which have bee.n already organized ; and they are consequently dependent, 

 either directly or indirectly, upon the Vegetable kingdom, for their means of 

 support. Now they cannot incorporate any. alimentary substance into their 

 own tissues, until it has been reduced to the fluid form ; hence they need the 

 means of effecting this reduction, which are supplied by the stomach. Again, 

 they cannot be always in immediate relation with their food ; they have to 

 go in search of it, and need a store-room in which it may be deposited during 

 the intervals ; this purpose also is supplied by the stomach. It is evident,' 

 moreover, that the powers of voluntary locomotion and sensation, which Ani- 

 mals enjoy, are connected with the peculiar nature of the food they require ; 

 for if they were fixed in the ground, like Plants, they would not be able to 

 obtain that which they require for their support. It is true that there are 

 some which seem almost rooted to one spot ; but these have the power of 

 bringing their food within their reach, though they cannot go in search of it. 

 Such is the case with many Polypes, which use their outspread tentacula for 

 this purpose ; and with the lower Mollusca, which can create currents by 

 means of ciliary action. 



15. A distinction might probably be erected between the Animal and Vege- 

 table kingdoms, upon the mode in which the first development of the germ 

 takes place. The seed of the Plant, at the time of fertilization, principally 

 consists of a store of nourishment prepared by the parent for the supply of the 

 germ, Avhich is introduced into the midst of it. The same may be said of the 

 egg of the Animal. In both instances, the first development of the germ is 

 into a membranous expansion, which absorbs the alimentary materials with 

 which it is in contact ; and it prepares these by assimilation, for the nourish- 

 ment of the embryonic structure, the most important parts of which, in the 

 higher classes of Animals and in Phanerogamic Plants, the only permanent 

 parts are in its centre. Now in Plants, this membranous expansion (the 

 single or double cotyledon) absorbs -by its outer surface, which is applied to 

 the albumen of the seed, and takes it more or less completely into its own 

 substance. In Animals, this expansion is developed in such a manner, that 

 it surrounds the albumen, enclosing it in a sac, the inner surface only of which 

 is 'concerned in absorption. The sac is, then, the temporary stomach of the 

 embryonic structure ; it becomes the permanent stomach of the Radiata ; but 

 in the higher classes, only a portion of it is retained in the fabric of the adult, 

 the remainder being cast offj like the cotyledon of Plants, as soon as it has 

 performed its function. Thus, then, the first nisus of Animal development is 

 towards the formation of a stomach, for the internal reception and digestion of 

 food ; whilst the first processes of Vegetable evolution tend to the production 

 of a frond-like membrane, which, like the permanent frond of the lower classes 

 of Plants, absorbs nourishment by its expanded surface only. 



