INTERNAL ANATOMY. 343 



delicate branch to the peritoneum, another, 2bl, branching to the distal end 

 of the large hermaphroditic duct and to the peritoneum of the vesicle of Swam- 

 merdam, and then bifurcates equally. One of the branches thus formed, 2b4, 

 curves to the left and upward around the anterior border of the adnexed genital 

 mass and penetrates the dorsal body-wall above the latter. Here it gives off 

 slender branches to the vesicle of Swammerdam and to the peritoneum. The 

 main trunk penetrates among the muscles forming the floor of the pericardial 

 cavity, courses obliquely backward to its posterior wall, in which it again ascends 

 to recurve obUquely to the right in the roof of the pericardium. It innervates 

 the floor of the pericardium, the anterior end of the crista aortae, the beginning 

 of the auricle, the roof of the pericardium, the reno-pericardial opening and 

 its tube, and the kidney. The other branch, or genital nerve, SbS, passes directly 

 backward and across the base of the adnexed genital mass to the genital ganglion 

 group, g. g. This latter complex is shown on Plate 5 in fig. 4, g. g, and in more 

 detail on a larger scale in fig. 1 of the same Plate. Here the delicate con- 

 nective-tissue investment of the distal end of the small hermaphroditic duct has 

 been dissected away, exposing the whole group of genital gangUa. Two of 

 these, gl and g2, are fairly conspicuous (Plate 5, fig. 4), but the remaining 

 ones, gS and g4, require careful dissection under high magnification for their 

 detection. The genital nerve, g. n, the branch of the second visceral nerve just 

 described, terminates in the largest of these genital gangUa, gl, from which the 

 nerves, a, pass into the adjacent dorsal peritoneum, and the nerve, b, is sent to 

 the small hermaphroditic duct. The remaining ganglia, g3, g3, and g4, are con- 

 nected with gl in a complicated plexus from parts of which the nerves, c, pass on 

 to the small hermaphroditic duct and the ovotestis, while the fine branches d, 

 together with other stiU finer ones not figured, penetrate the adnexed genital mass. 

 Figure 1 of Plate 3 illustrates the parieto-visceral complex of Tethys cervina, 

 as described by the writer (1909). It is here introduced to call attention to the 

 homologies existing between this representative of the Aplysiinae and Dola- 

 bella agassizi. Comparing this with Plate 3, fig. 2 it is seen that the two visceral 

 nerves in Dolabella represent the four shown in Tethys cervina, the second one 

 in Dolabella being formed by the union of the second, third, and fourth of 

 Tethys. Identical relations in the visceral innervation of the organ of Bohadsch 

 and in the anastomosis of a branch of the second visceral with a pedal nerve 

 are also evident, so that the double innervation of this organ from both visceral 

 and pedal gangUa obtains in this subdivision of the family Aplysiidae, as well 

 as in the more restricted Aplysiinae. 



