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 Uning 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 2G.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 alUed 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 mamfestly 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 



