in the Animal Kingdom. 125 



central portions of systems. This separation into textures, is the 

 " histological separation. 



Besides the above, there arise differences in outward shape ; 

 single sections of the tubes being developed into distinct forms 

 or organs, destined to perform particular functions ; which func- 

 tions are subordinate members of the function of the whole tube ; 

 but differ from the functions of other sections of the latter. For 

 example, the mucous tube divides itself into the mouth, oeso- 

 phagus, stomach, intestine, respiratory apparatus, liver, urinary 

 bladder, &c. ; the peculiarity in the development being connected 

 with either an increased or diminished growth. This is the 

 " morphological" separation. 



Thus, by a threefold division, the mass becomes heterogene- 

 ous ; and the further back we go, the more do we find, not sin- 

 gle organs only, but histological elements united. 



" Fresh parts are acquired, not by new, but by transforma- 

 tion. When, for example, the foundation of a cartilage forms, 

 there was not previously a vacancy in the place it occupies, but 

 a homogeneous mass; the change in which, consists in the ap- 

 pearance of an assemblage of opaque granules, and a surround- 

 ing pellucid fluid. This is the manner of histological separa- 

 tion ; calling forth, as it were, antitheses." 



" No part is formed, that was not previously in connexion with 

 some part, earlier formed ; no part has an isolated origin, then 

 adding itself to the rest. Nothing swims freely around, annexing 

 itself here or there, as formerly was said of the whole embryo, 

 and even lately, has been conceived and taught of the spinal 

 cord.* Each organ is a modified part of a more general organ ;"' 

 and development proceeds from the centre towards the periphery. 

 This is the manner of morphological separation. 



It was to uniformity in the manner of the primary, of the 

 histological) and of the morphological separations, just described, 

 that we referred in the proposition, that essentially the manner 

 of the metamorphosis, or metamorphoses i. e. the manner of 

 development from a more homogeneous or general, to a more 



* Such is the doctrine of Serres. See his " Anatomie Compare du Cer- 

 veau ;" also his " Recherches d' Anatomic Transcendante et Pathologique." 

 4to, 1832. 



