ON THE STAGES OF EVOLUTION 227 



rectal digestion, as bereft of almost all the attributes of 

 a digestive process, although, from clinical experience, we 

 have learned, that even the rectal mucosa is capable of 

 absorbing ready-prepared nutritive matter, and can be 

 relied upon to do so in certain suitable emergencies. 



The enteric canal, thus, remains patent, or hollow, and, 

 passes through it the food which is to serve for the 

 nutriment of the body, the compartments, into which it is 

 divided, serving for specific parts of the digestive process, 

 and the absorption, of specific elements of nutrition, by 

 the various local mucosae. Many of the glands, and a 

 number of the principal viscera, empty themselves into it, 

 adding digestive elements, and excreting, it may be, certain 

 effete matters, for removal from the body. 



At its interior and posterior, extremities, it is in a 

 modified form, still connected with its former neural half, 

 and affords a means of exit for the disposal of super- 

 abundant cerebro-spinal fluid, which continues to represent 

 the fluid with which it was originally occupied, and which 

 it continues to utilise both for mechanical and physio- 

 logical, purposes. 



The neural half of the neurenteric canal, is almost 

 completely occupied, as we have already said, by the 

 systemic nervous system, which has grown into it, and 

 then pushed before it, by every axonal fibre, or process, 

 which grows out of it, a continuation of its meningeal 

 coverings, into every hole and corner of the body, inner- 

 vated by that system, as a protection, or inhibiting wall, 

 in the form of neurilemma and perineurium, or meningeal 

 continuation. 



The neurally unoccupied part of the canal, is, therefore, 

 represented by the ventricles of the brain, the central 

 canal of the cord, the sub-arachnoid and sub-dural, spaces, 

 centrally, and by the intra-neurilemmar spaces of the 

 nerves, peripherally, all these spaces, being continuous, the 

 one, with the other, and all occupied by the cerebro-spinal 

 fluid, the representative of the original neurenteric fluid, 

 which occupied the undifFerentiated neurenteric canal. 



The systemic nervous system, has, therefore, projected 

 itself, along the lines of least resistance, into the meso- 

 dermic, and hypodermic, areas of the body, becoming 



