The chief feature in which Peripatus was supposed to differ from normal Arthropoda and Annelida, viz. the absence of ganglia on the ventral cords, does not really exist. In other particulars, as in the amount of nerve cells in the ventral cords and the completeness of the commissural connections between the two cords, &c., the organisation of the nervous system of Peripatus ranks distinctly high. The nervous system lies within the circular and longitudinal muscles, and is thus not in proximity with the skin. In this respect also Peripatus shews no signs of a primitive condition of the nervous system.
A median nerve is given off from the posterior border of the supra-œsophageal ganglion to the œsophagus, which probably forms a rudimentary sympathetic system. I believe also that I have found traces of a paired sympathetic system.
The organ doubtfully spoken of by Mr Moseley as a fat body, and by Grube as a lateral canal, is in reality a glandular tube, lined by beautiful columnar cells containing secretion globules, which opens by means of a non-glandular duct into the mouth. It lies close above the ventral nerve cords in a lateral compartment of the body-cavity, and extends backwards for a varying distance.
This organ may perhaps be best compared with the simple salivary gland of Julus. It is not to be confused with the slime glands of Mr Moseley, which have their opening in the oral papillæ. If I am correct in regarding it as homologous with the salivary glands so widely distributed amongst the Tracheata, its presence indicates a hitherto unnoticed arthropodan affinity in Peripatus.
[458] From the Proceedings of the Cambridge Philosophical Society, Vol. III. 1879.
[459] “On the Structure and Development of Peripatus Capensis,” Phil. Trans., Vol. CLXIV. 1874.
[460] “Bau von Perip. Edwardsii,” Archiv f. Anat. u. Phys. 1853.
[461] Moskauer Naturforscher Sammlung, Abth. Zool. 1869.
[462] This was known to Grube, loc. cit.
[463] These nerves were noticed by Milne-Edwards, but Grube failed to observe that they were much larger than the nerves given off between the feet.