ALEXANDROMENIA AGASSIZI. 141 



delicate branches. Usually the most anterior connective is of the largest calibre, 

 but in the present instance the first two or three are extremely tenuous, not over 

 one third the diameter of the succeeding connectives. Dorsal nerves from the 

 lateral ganglia are numerous but in no instance have they been traced to the 

 mid dorsal line. 



The labio-buccal system is probably more extensive than is shown in Plate 12, 

 fig. 5, for owing to tlie great width of the muscular joharynx and the abundance 

 of salivary glands closely crowded together it is very difficult to trace nerves for 

 any considerable distance. The connectives may be readily followed to the 

 ganglia at the sides of the pharynx, and the commissure uniting these is as readily 

 demonstrated, but a different state of affairs is met with elsewhere. Before 

 uniting with the la]:)io-buccal ganglia the connectives far out on the external face 

 of the salivary glands enter a ganglionic enlargement on each side from which 

 two nerves originate. One of small size disappears almost immediately among 

 the glands; the other of much larger size passes in toward the mid line, Ijut Ije- 

 comes lost in the darkly staining secretion of these same glands. From the 

 dorsal side of each labio-buccal ganglion a small nerve arises that gradually 

 extends to the lateral border of the pharynx which it crosses to form a com- 

 missure. At various points throughout this entire system exceedingly small 

 nerves arise and probably innervate the neighboring regions but their destina- 

 tion is not certain. 



In the ]:)osterior end of the body the lateral nerves become so crowded 

 against the body wall, owing to the huge shell gland, that it has been impossible 

 to trace connectives in this region. Opposite the posterior end of the heart they 

 expand greatly (Plate 12, fig. 6), and originate several nerves distributed more 

 posteriorly as well as the suprarectal commissure. Two connectives, the pos- 

 terior one of large size, unite with the posterior end of the pedal cords. In the 

 mid line the suprarectal commissure develops a nerve that passes to the base of 

 tiie dorso-terminal sense organ, to which it sends a small nerve, whereupon it 

 proceeds backward distributing fibres to the dorsal gill plates. The large 

 branches, springing more laterally from the posterio-lateral enlargements, 

 branch repeatedly and in many places delicate offshoots have been found enter- 

 ing the branchial folds. Plate 12, fig. (> represents the more important of these 

 whose number ami origin is correctly shown though the branching is somewhat 

 diagrammatic. With this exception the nerves and ganglia shown are recon- 

 structed carefully from micrometric measurements. 



The pedal ganglia have not been examined in the middle of the body, but 



