THE CHAIN OF SPECIES. 465 



show is probably already a compound of many removes from the 

 beGfinninoj. 



The la^v of compounding is not at all mysterious. If the first force 

 of reproduction, the genesis of individuals, exhibits itself in the form 

 of an evolution — a budding forth, a repetition of the form and struct- 

 ure of the parent cell — the law of compounding first presents itself as 

 an arrestation of the law of gemmation. The old cell fails in force 

 to throw off the new one ; or, by another law, equally in force, adhe- 

 sion takes place between the contiguous surfaces of the old and the 

 new, and the extrusion to complete independence cannot be effected. 

 This is the simple rule extending up through all the shining ranks and 

 files of life. In the higher forms this law presents itself in the form 

 of involution ; but in lower creatures it is but an adhesion — an anchy- 

 losis. In all it is 2i failure of a perfect evolution — a failure perfectly 

 to develop and reproduce a separate cell. 



Xow that we have the laws, let us see if we comprehend their ap- 

 plication in jN"ature's workings. Really we might go to mathematics, 

 and take from geometry, not only illustrations, but the very defini- 

 tions of biology. Geometry, first and simplest of the sciences, begins 

 its definitions with a point ; from a point it j^roceeds to a line ; from a 

 line to a surface ; from a surface to a solid. In biology, beginning 

 with a cell, which is the jjhysiological point or unit ; the next devel- 

 opment is to an axis, a line of cells, the type of all baculate struct- 

 ures. This baculus revolved upon itself, phyllate structure — a biologi- 

 cal surface, the type of all organisms having one depth of cells. The 

 next step is to the biological solid. This is made by an involution, a 

 folding down of the surface upon itself, constituting a creature of two 

 laminse — tw^o tiers of cells. 



Passing on to another class, typically displayed for instance in 

 hepaticse, we find that another involution has taken place. This time 

 the phyllum of two tiers of cells is folded upon itself, constituting one 

 normally of four layers. Here first occur those curious openings into 

 the centre of the structure known as stomata, rendered necessary, of 

 course, from the fact that two of the strata are internal, and but for 

 these contrivances would be cut off from that direct contact with at- 

 mospheric air which is necessary to the life of external living creatures. 

 The next and the last evolution which takes place in the ascending 

 development of plants is the folding upon itself of this leaf of four 

 thicknesses of cells, so as to make a sheet consisting essentially of 

 eight thicknesses of cells — the type of all the so-called higher plants. 

 In this respect exogens and endogens do not differ ; their only real 

 difference being the atrophy and suppression of one cotyledon of the 

 former to constitute the latter. In exogens there may be, in addition 

 to these, various subordinate adhesions, but no further involutions of 

 the whole creature. These may be called topical, as affecting only 

 portions of the compound structure ; and among endogens, from the 



VOL. Y.— 30 



