344 i THE DOLABELLINAE. 
Parietal nerves.—The first parietal, or vulvar nerve (Plate 3, fig. 2, p. 1) : 
arises from the ventral surface at the left or posterior end of the ganglion. It — 
emerges from the capsule between the two ganglionic components of the parieto- 
visceral group, but slightly nearer the parietal one, into which it can be traced. 
It passes backward in the connective-tissue attached to the aorta (Plate 4, 
fig. 1, p. 1) to the dorsal body-wall, and thence directly to the anterior end and 
external opening of the large hermaphroditic duct. It gives off a branch later-— 
ally, which curves to the right and forward, uniting with the branch 7a from the 
seventh pedal nerve, which is distributed to the organ of Bohadsch, which rela- 
tion is the same as that found in Tethys cervina (Plate 3, fig. 1), the pedal nerve _ | 
in that instance being the third in serial order. y 
From the posterior end of the right parietal ganglion arises a single strong — 
nerve, the second parietal, or osphradio-ctenidial nerve. Its general relations — 
are shown in Plate 3, fig. 2, p2, and the detail of its ramification in Plate 4, 
fig. 1, p2. It curves backward along the left border of the aorta, crosses above 
it, and opposite the middle of the V-shaped heart penetrates the dorsal peri- 
toneum, giving off the following branches:— Plate 4, fig. 1, 7, a slender nerve to 
the peritoneum, 2, a nerve which passes directly forward near the median line 
below the spermatic furrow, to which it ramifies, also sending off the branch 2a, 
which fuses with a branch of the 7th pedal nerve, 7p. The main trunk is 
markedly thickened near the origin of these branches, and bifureates into the 
nearly equal divisions 3 and 4. The ramus 3 forks into 4 and 6, the first pass- 
ing to the anterior portion of the mantle, the second to the outer face of the 
kidney, giving off the branch 7 to the ventral face of the same organ. The 
ramus 4 thickens decidedly, though no well-marked ganglion is formed, and 
gives off the branches 8 and 9 to the walls of the venous sinus at the base of the 
heart and to the mantle, and also numerous delicate short twigs which pass © ; 
through the integument to the osphradium, at the anterior end of the ctenidium, ~ 
indicated in the figure cited by the outline osp. Beyond the thickened portion — 
the main nerve gives off the branch /0, which ramifies to the roof of the branchial 
- chamber above the ctenidium, and to the walls of the branchial sinus at its base. 
The main nerve-trunk 1/7, now enters the ctenidium and continues as its chief 
ctenidial nerve, cl. n, along the greater curvature to its tip, giving off numer- 
ous lateral branches to its different divisions. Other than the smoothly out- 
lined thickening indicated above there is no trace of a distinct osphradial or | 
ctenidial ganglion. . 
ResprraTorY, CrrcuLaATory, AND ExcretTory Systems.— The external - | 
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