The facts now recorded were discovered in June last, only a short time before Balfour started for Switzerland; we know but little of the new ideas which they called up in his mind. We can only point to passages in his published works which seem to indicate the direction which his speculations would have taken.
After speculating as to the probability of a genetic connection between the circumoral nervous system of the Cœlenterata, and the nervous system of Echinodermata, Platyhelminthes [TN23], Chætopoda, Mollusca, &c., he goes on to say:
“A circumoral nerve-ring, if longitudinally extended, might give rise to a pair of nerve-cords united in front and behind—exactly such a nervous system, in fact, as is present in many Nemertines (the Enopla and Pelagonemertes), in Peripatus and in primitive molluscan types (Chiton, Fissurella, &c.). From the lateral parts of this ring it would be easy to derive the ventral cord of the Chætopoda and Arthropoda. It is especially deserving of notice, in connection with the nervous system of the above mentioned Nemertines and Peripatus, that the commissure connecting the two nerve-cords behind is placed on the dorsal side of the intestines. As is at once obvious, by referring to the diagram (fig. 231 B), this is the position this commissure ought, undoubtedly, to occupy if derived from part of a nerve-ring which originally followed more or less closely the ciliated edge of the body of the supposed radiate ancestor.” (Comparative Embryology, Vol. II. pp. 311, 312, the original edition[577].)
The facts of development here recorded give a strong additional support to this latter view, and seem to render possible a considerable extension of it along the same lines.]
List of Memoirs on Peripatus.
1. M. Lansdown Guilding. “An Account of a New Genus of Mollusca,” Zoological Journal, Vol. II. p. 443, 1826.
2. M. Andouin and Milne-Edwards. “Classific. des Annélides et description de celles qui habitent les côtes de France,” p. 411, Ann. Scien. Nat. ser. I. Vol. XXX. 1833.
3. M. Gervais. “Études p. servir à l'histoire naturelle des Myriapodes,” Ann. Scien. Nat. ser. II. Vol. VII. 1837, p. 38.
4. Wiegmann. Wiegmann's Archiv, 1837.
5. H. Milne-Edwards. “Note sur le Peripate juluforme,” Ann. Scien. Nat. ser. II. Vol. XVIII. 1842.