946 » REPORT—-1896. | 
system of the vertebrate must be considered as derived from the conjoined central 
nervous system and alimentary canal of an arthropod. 
Comparison of the Central Nervous System of Ammocetes with the 
Conjoined Central Nervous System and Alimentary Canal of an 
Arthropod Animal such as Limulus. 
1. The phylogenetic test proves that the tube of the central nervous system was 
originally an epithelial tube, surrounded to a certain extent by nervous material. 
The anatomical test then proves that this epithelial tube corresponds in its 
topographical relations to the nervous material exactly with the alimentary canal 
of an arthropod in its relations to the central nervous system ; and, further, that the 
topographical relations, structure, and function of the corresponding parts of this 
nervous material are identical in the Ammocecetes and in the arthropod. 
We see from these diagrams, taken from Edinger, how the greater simplicity of 
the brain region as we descend the vertebrate phylum is attained by the reduction 
Fig. 2.— Dorsal and Lateral view of the Brain of Ammoccetes. 
of the nervous material more and more to the ventral side of the central tube, with 
the result that the dorsal side becomes more and more epithelial, until at last, as is 
seen in Ammoceetes, the roof of the epichordal portion of the brain consists 
entirely of fold upon fold of a simple epithelial membrane, interrupted only in one 
place by the crossing of the [Vth nerve and commencement of the cerebellum. 
In the prechordal part of the brain this simple epithelial portion of the tube is 
continued on in the middle line as the first choroid plexus of Ahlborn, and the 
lamina terminalis round to the ventral side; where, again, in the infundibular 
region, the epithelial saccus vasculosus, which has been becoming more and more 
