70 Traces of Unity in the 



their entire length by caecal prolongation of the stomach, 

 the limbs and the caecal prolongations within them being 

 very nearly of the same dimensions as the narrow limb- 

 like body and the narrow alimentary canal within it. 

 Or, to take a more familiar case, it is almost impossible 

 to watch a worm or snake in motion without being con- 

 vinced that the body here is scarcely less limb than 

 body. 



If, then, it be true that animals agree with plants in 

 that no clear line of demarcation is to be drawn between 

 the central parts of the body and the append icular 

 parts, what is to be said about the archetypal idea of 

 these parts ? Is it necessary to try and apply the notion 

 of the annellus or the vertebra to the interpretation of 

 the appendicular parts, or is it necessary to try and find 

 in these latter parts another and simpler archetype which 

 may contain and explain the annellus and vertebra ? The 

 appendicular parts may be regarded as representing a 

 more simple phase of development than the central 

 parts, and, therefore, it is to be expected that the latter 

 alternative is that which must be accepted. And, to say 

 the least, the result of examining the appendicular 

 organs with this end in view is very significant. 



Taking the eye of the eagle as the exemplar of ap- 

 pendicular organs, and using it as a text, it may be 

 noticed first of all that the coats of this organ are com- 

 posed of several laminae or layers, nervous, vascular, 

 quasi-muscular, osseous and others, arranged concentri- 

 cally the one within the other, so as to form a hollow 

 sphere, open to the front, or rather only closed in that 

 direction by a transparent window. All the several 

 layers mentioned are evidently arranged upon the same 

 plan : the osseous layer is a simple ring made up of seg- 

 ments fitted together like the staves of a shallow tub 



