TETHYS DACTYLOMELA (rANG) 23 



it passes in a sinuous course to the anus, situated upon the poste- 

 rior wall of the siphon. At the beginning of the intestine its 

 dilated lumen receives two large biliary ducts, which ramify- 

 throughout the substance of the liver. Two low ridges, bounding 

 a shallow groove, lie along the intestinal wall in contact with the 

 liver, near the beginning of the tube. These may be followed 

 backward into a long curved blind tube, in the wall of which they 

 become overlapping elevations, dividing it into two longitudinal 

 chambers which are in communication at the end of the tube. 

 This, the hepatic coecum, is imbedded in the substance of the 

 liver throughout nearly its whole length, but its blind termination 

 reappears at the surface as a small rounded area, which might 

 readily be mistaken for a portion of the wall of the intestine. 

 The coecum describes a C shaped loop of nearly lo.o mm. in 

 length with a fairly constant diameter of 1.5 mm. 



Central Nervous System. 



The ganglia. The central nervous system of Tethys dacfy- 

 lomela (PL II, fig. 8) is made up of eight paired ganglia grouped 

 around the anterior end of the esophagus, close to its origin from 

 the pharyngeal bulb. These are the cerebral, the pleural, the 

 pedal and the buccal ganglia, the right and left components of 

 each pair being united by commissures, while the ganglia of each 

 side are united by the cerebro-pedal, the cerebro-pleural, the 

 cerebro-buccal and the pleuro-pedal connectives. In addition to 

 these centrally located ganglia, there are others, more or less 

 distant from the central system. Chief of these are the parieto- 

 visceral, the genital, and the ganglia of the anterior and the poste- 

 rior tentacles. The central nervous system is closely enveloped 

 by a capsule of connective tissue in a firm sheath, which renders 

 the dissection of the nerves a matter of some difficulty. The 

 ganglia, their commissures, connectives and nerves will be taken 

 up in order in the following description. The figures and de- 

 scriptions given by Von Ihering {'77), Mazzarelli ('93), and 

 Vayssiere ('85), based upon European species of Tethys, vary 

 so much from the results which I have obtained in Tethys dacty- 

 lomela and in T. cervina that considerable detail seems to be justi- 

 fied in the following account. In fig. 8 of PI. II I have endeavored 

 to give an accurate representation of the central nervous system 



