338 THE DOLABELLINAE. 
toneum of these regions. It also forms an anastomosis with a branch of the 
left posterior pedal nerve, 9a, in a position similar to that entered into by its 
fellow of the opposite side. 
From the loop of the parapedal commissure, a little to the left of its middle 
point, a slender unpaired nerve, c, is given off. It courses backward along 
the ventral surface of the head retractor muscles to a point below the anterior 
end of the ingluvies, where it curves downward and backward through the con- 
nective-tissue septum to the foot, ramifying there in the peritoneum. 
Of the above nerves the second unpaired one was described by Amaudrut 
(1886) for Dolabella, and has been noted in various species of Tethys by Cuvier — 
(1804), Von Ihering (1877), Vayssiére (1885), Mazzarelli (1893), and the writer 
(1909). The paired nerves here described as arising from the parapedal com- 
missure have not been found heretofore in any member of the group. It may 
possibly be a case of a fusion of a pedal nerve with the beginning of the com- 
missure to such an extent that it appears to be a branch of the latter on leaving 
it, for the nerve-cells from which the fibres spring are without doubt to be 
found in the pedal ganglion itself. 
Pleural ganglia.— The pleural ganglia rest upon the upper posterior face 
of the pedal ganglia, to which they are united by extremely short pleuropedal 
connectives. They are inclosed with the pedal ganglia in a close common invest- 
ment of connective-tissue, so that they are not distinguishable until after care- 
ful dissection and clearing. They are ellipsoidal in form, strongly flattened 
dorso-ventrally, and about one fourth the size of the pedal ganglia, measuring 
approximately 1.3 mm. in width by 1.9 mm. in length. From the upper outer 
face of each ganglion is given off the strong cerebro-pleural connective, which, 
at first independent, soon joins the cerebro-pedal connective and passes around 
the oesophagus with it to join the cerebral ganglia on the dorsal side. 
Pleural nerves.— Each of these pleural ganglia gives rise to two nerves. 
The first pair of these (Plate 2, fig. 1, pl. 1), arise from the antero-lateral face — 
of the ganglia immediately in front of the origin of the cerebro-pleural con- 
nective. It is very delicate and passes outward, joining the third pedal nerve ~ 
in a common sheath and has a common distribution with it, as already given 
above in the description of the nerves from the pedal ganglia. 
From the inner posterior border of each pleural ganglion arises a long 
and strong connective, each passing back to unite with a peripheral group of 
ganglia, forming the visceral loop. That of the right side is the pleuro-parietal 
connective, pl-par. con, that of the left the pleuro-visceral connective, pl-v. con. 
