THE CHAIN OF SPECIES. 569 



if amphioxus is a vertebrate animal, which is exceedingly doubtful. 

 But the difficulty is to get to cephalopods. 



It is confessedly easy to pass from the coelenterate type to the an- 

 nulose — or, in the old style, from JRadiata to Articulata. 



ISTothing is more manifest in Nature than that she never loses the 

 effect of a habit — never gives up a plan — never resigns the use of 

 means and tools once adopted. When we have arrived at the involute 

 cell as the type of the endothentic series — the animal kingdom — noth- 

 ing is more obvious than the compounding of the simple form to con- 

 stitute the rest of the kingdom. Nor is it necessary to suppose that 

 the compounding takes place by any other means than that already 

 observed in the case of exothentic creatures. If vegetal cells multiply 

 and compound by a gemmating and fissiparous process, so also does 

 the endothentic and celoenterate type. 



Mr. Spencer has shown, triumphantly, how this may take place 

 even mechanically. A simple endothen becomes two by ordinary 

 growth, until division is forced at some median point, exactly as in the 

 case of a cell. When the separation is complete we say this is an in- 

 crease by gemmation. When there is differentiation without separa- 

 tion, we call it compounding — or, as Mr. Spencer has it, an aggrega- 

 tion. The same two great laws of aggregation and segregation, which 

 rule in all things else, present themselves here also in explanation of 

 the phenomena of life. As presented in annulose and annuloid creat- 

 ures, the compounding is a segmentation. For an annulose or articu- 

 late segment is nothing else but one of the simple elements of a com- 

 pound structure, of which the distinction of the parts is less pronounced. 

 In sponges, in corals, in compound ascidians, the segregation is far 

 advanced — the compounding is very evident. In these it is not denied 

 any more than in the analogous compounding displayed in mosses, 

 ferns, and trees. For, according to the laws of vegetal life already 

 reviewed, every leaf, every node, is a distinct creature, and the bud 

 of the node its progeny. But it is not at first sight so obvious that 

 the real law of all creatures constituted of rings and joints is the law 

 of compound association. It is difficult, without some reflection, to 

 admit that every segment in these is a modification of the original 

 unicellular creature — the mono-segmentarian from which the aggre- 

 gation sprang. Yet the most casual anatomist cannot fail to perceive 

 that each section in annulosa is but a repetition of the same structure 

 with all its organs and appendages. Even where there are modification 

 and differentiation of function, the structure is always and evidently 

 identical — perfectly homologous. 



Fully comprehending the nature of segments, we may proceed to 

 the further efforts of Nature to obtain higher combinations and greater 

 concentrations of energy. For this seems to be the end and object 

 aimed at, if we may be allowed in our own minds to clothe Nature 

 with conscious impersonation, i. e., personality. From the organization 



