PREFACE. IX 



body, and most end there ; but no special anatomy can be rightly 

 and fully understood save on the basis of the general science of 

 wliich it is an integral part. The reason lies in the diversities of 

 organic structure being subordinated to a principle of unity. Of 

 this principle, apprehended as an ' idea ' or truth of reason, the 

 understanding receives evidences in number and comprehen- 

 sibihty differing in different natural groups of the animal king- 

 dom. Illustrations of the ' idea ' will be found in the chapters on 

 the Articulate Province and other parts of the ' Lectures on In- 

 vertebrates,' and, in accordance with the present phase of ana- 

 tomical science, more abundantly in the present Work. True it is 

 that in the first steps to organisation we seem to see a tendency to 

 disintegration, to a reduction of the i)rimary whole to the sub- 

 ordinate characters of a part. The first centre of sarcode, or 

 undifferenced oi'ganic matter, however originated, yet with de- 

 finite tendencies to formal character and course of growth (as in a 

 Foraminifer, e.g.), buds forth a second centre of identical nature; 

 this a third, and so on, until a group of such exists as an assem- 

 blage of coherent homogeneous or like parts. These, if clothed by 

 a delicate crust of characteristic structure, constitute a chambered 

 shell, straight, bent, or spiral, each chamber occupied by the 

 same vital sarcode, outshooting filamentary food-getting processes 

 through the shell-pores ; in which seeming comjjlexity the inci- 

 pient unity or ' wdiole ' is reduced to the ' part ' called innermost 

 chamber, or is conceivable as a lesser whole in the larger one. 

 The Annelides offer a familiar example of such repetitions of a 

 pi'imal complexly organised whole, by successive buddings in a 

 linear direction ; the nerve-centre, the muscles, the skeleton-seg- 

 ment, perhaps heart and gills, being regularly repeated in each, 

 and thereby reducing the original whole to one of many parts of 

 a segmented unit}^ 



Almost every organ in the pi'ogressively differenced organism 

 initiates itself under a similar cliaracter of irrelative rej^etition, 

 suggestive of operance akin to that of inorganic polar growths, as 

 in a groujj of crystals, wherein each exemplifies the characters 



