644 'Journal of Comparative Neurology and Psychology. 



lobes, and almost immediately unite in the broad stout band known 

 as the first ventral commissure, V-^', they then extend backward, 

 and with a decrease in size become the lateral cords of the body. 

 The two proboscis nerves, pr n, originate on the anterior surface 

 of the first ventral commissure and pass forward and upward into 

 the proboscis at its attachment. From the lateral surfaces of both 

 dorsal and ventral lobes, nerves, not shown in this figure, are 

 given off at irregular intervals, and are not paired with those of the 

 opposite side. The dorsal lobes end posteriorly in the cerebral 

 sense organs, not shown in this figure, which in their turn termin- 

 ate just in front of the anteriorendof the mouth. The oesophageal 

 nerves, E N, arise within the fibrous core of the ventral lobes as 

 follows: A small portion on the medial surface of each brain 

 lobe is constricted off from the rest by a delicate septum, the nerve 

 sheath. These separated portions are the two oesophageal nerves, 

 which, for a short distance, lie within the fibrous sheath of the 

 brain, but farther back pierce the sheath and assume a more 

 medial position. 



Behind the broad first ventral commissure comes a series of 

 commissures, 2 to J^, giving a ladder-like appearance to the brain. 

 Closer investigation reveals thirteen of these commissures, some 

 of which, coming only from the cellular sheath of the brain, may 

 represent the metameric commissures described by Hubreght, 

 but others of which, having their roots in the fibrous core of the 

 brain, are commissures that have not been previously described. 

 According to their origin the commissures are of three different 

 kinds: (i) those running from ventral lobe to ventral lobe, whether 

 from the fibrous core or from the cellular sheath, brain commis- 

 sures; (2) those running from ventral lobe to ventral lobe and 

 traversing the substance of the oesophageal nerves, brain-cesoph- 

 ageal commissures; (3) those running between the oesophageal 

 nerves only, (esophageal commissures. 



As many of the commissures are figured here for the first time, 

 they will be described with considerable detail. Their clearness 

 and distinctness are evidently due to the size and the extension of 

 the very favorable material. The following table is a summary 

 of the position, thickness and character of the commissures. 



