INTERNAL ANATOMY. 329 
groove passes, is continued along its inner surface to the base of the penis, and 
recurves along the latter to its tip. The margins of the groove are formed by 
two thin and prominent folds of the integument, inclosing a narrow V-shaped 
furrow between them. Immediately above this groove at the external opening 
of the penis-sheath a higher and more fleshy fold of its lining projects into its 
lumen, and extends backward throughout nearly the whole length of the sac, 
becoming lower and less conspicuous from the middle of its length backward. 
Numerous other lower, smaller, and more irregular folds may also be traced 
along the lining of the sheath for varying distances. The general color of the 
epidermis of the organ is a dark brown, or even black, the pigmentation extend- 
ing back to about 10 mm. of the bottom of the sheath. The penis, or more 
exactly, the glans-penis proper, is slender, flattened throughout and pointed 
at the tip. It is 26.5 mm. long and 5.0 mm. wide at its base. Together with 
the eversible praeputium, or penis-sheath, the whole organ attains a length 
of 76.0 mm. The color of the glans is uniformly light yellow and it is destitute 
of any armature whatever. 
Nervous System.— But little study seems to have been made upon the 
nervous system of Dolabella, the allied genera Tethys and Notarchus having 
fared much better in this respect. Aside from a brief paper without figures by 
Amaudrut (1886), the studies of Lacaze-Duthiers (1898) upon the buccal 
(“stomatogastric’’) ganglia and nerves, and very fragmentary notes by Bergh 
(1905, 1907), no observations have been recorded upon the nervous apparatus 
of this form, since the first studies of Cuvier (1804). Lacaze-Duthiers (1898) 
presents good detailed figures dealing with the distribution of the sympathetic 
nerves of Dolabella scapula in comparison with Tethys (Aplysia) depilans, and 
Bergh (1905) gives a rough and manifestly incomplete figure of the central 
ganglia of D. rumphii [= scapula]. It has, therefore, seemed very desirable to 
devote considerable attention to these structures in the Easter Island species. 
Central nervous system.— The general features of the nervous system of 
Dolabella agassizi are similar to those characteristic of the Aplysiidae in general. 
Four pairs of large ganglia, the cerebral, pleural, pedal, and buccal are grouped 
around the posterior end of the pharyngeal bulb. The members of three of 
these pairs, the cerebral, pedal, and buccal are united above or below the 
oesophagus by commissures of different lengths, and the cerebral, pedal, and 
pleural ganglia of each side are united by connectives into the familiar triangular 
grouping, characteristic of the Gasteropoda in general. In addition to these 
larger ganglia the parietal and visceral ones are fused into one common mass at 
ae 
