7 
: 
TRANSACTIONS OF SECTION I. 947 
conspicuous in the lower vertebrates, together with the median tube of the 
infundibulum, testifies to the withdrawal of the nervous material from this part of 
the brain, as well as from the dorsal region. Further, as already mentioned in my 
previous papers, the invasion of this epithelial tube by nervous material during the 
upward development of the vertebrate is beautifully shown by the commencing 
development of the cerebellar hemispheres in the dogtish; by the dorsal growth of 
nervous material to form the optic lobes in the Petromyzon ; by the occlusion of 
_ the ventral part of the tube in the epichordal region to form the raphé, as seen in its 
commencement in Ammoccetes. Finally, evidence of another kind in favour of 
_ the tubular formation being due to an original non-nervous epithelial tube is given 
by the frequent occurrence of cystic tumours, and also by the formation of the 
sinus rhomboidalis in birds. 
The phylogenetic history of the brain of vertebrates, in fact, is in complete 
harmony with the theory that the tubular nervous system of the vertebrate 
originally consisted of two parts—viz. an epithelial tube and a nervous system 
outside that tube, which has grown over it more and more, and gives not only no 
support whatever, but is in direct opposition, to the view that the whole tube was 
originally nervous, and that the epithelial portions, such as the choroid plexuses 
and roof of the fourth ventricle, are thinned-down portions of that nerve tube. 
Passing now to 
2. The anatomical test, we see immediately why this epithelial tube comes out 
so much more prominently in the lowest vertebrates, for, as can be seen from the 
diagrams, and is more fully pointed out in my previous papers,' every part of the 
central tube of the vertebrate nervous system corresponds absolutely, both in 
position and structure, with the corresponding part of the alimentary canal of the 
arthropod, and the nervous material which is arranged round this epithelial tube 
is identically the same in topographical position, in structure, and in function as 
_ the corresponding parts of the central nervous system of an arthropod. 
Especially noteworthy is it to tind that the pineal eye (PN), with its large 
optic ganglion, the ganglion habenule (GHR), falls into its right and appropriate 
place as the right median eye of such an animal as Limulus or Eurypterus. In 
the following table I will shortly group together the evidence of the anatomical 
test. 
A. Coincidence of Topographical Position. 
LIMULUS AND ITS ALLIES. AMMOC@®TES AND VERTEBRATES. 
Alimentary Canal :— 
1. Cephalic stomach. 
2. Straight intestine, ending in anus. 
Ventricles of the brain. 
Spinal canal, ending by means of the 
neurenteric canal in the anus. 
Median infundibular tube and saccus 
vasculosus. 
3. Gsophageal tube. 
Nervous System :— 
1. Supra-cesophageal ganglia. Brain proper, or cerebral hemispheres. 
2. Olfactory ganglia. Olfactory lobe. 
3. Optic ganglia of the lateral eyes. Optic ganglia of the lateral eyes. 
4. Optic gangliaof the median eyes. Ganglia habenule. 
5. Median eyes. Pineal eyes. 
6. Gsophageal commissures. Crura cerebri. 
7. Infra-cesophageal or prosomatic Hind brain, giving origin to the I[IIrd, 
ganglia, giving origin to the IVth, and Vth cranial nerves. i 
prosomatic nerves. 
8. Mesosomatic ganglia, giving origin Medulla oblongata, giving origin to the 
to the mesosomatic nerves. 
9. Metasomatic ganglia. 
VIlIth, [Xth, and Xth cranial nerves. 
Spinal cord. 
| ' Gaskell, Journ. of Anat. and Physiol. vol. xxiii. 1888; Journ. of Physiol. 
vol. x. 1889; Brain, vol. xii. 1889; Q. J. of Mier. Scr. 1890. 
a 
