84 GRIFFIN. 



surface is slightly convex, and is marked by fine parallel 

 ridges. The anterior angle is produced into a sharp, slightly 

 spiral point, from 4 to 6 millimeters in length, over which are 

 scattered small backw^ardly directed spines. Upon reaching the 

 base of the penis, the seminal furrow passes distally upon the 

 anterior surface of the cylindrical base of the organ and then 

 follows a somewhat spiral course to the tip of the prepuce. 



A shelf-like lamella springing from the right side of the 

 seminal furrow, which meets the overhanging margin of the 

 left side of the furrow, practically forms a closed tube along 

 the bottom of the seminal furrow for the passage of sperm from 

 the genital oriface to the copulatory organ. 



NERVOUS SYSTEM. 



The circumcesophageal ring formed by the central nervous 

 system is large and but loosely attached to the oesophagus. It 

 is enveloped by an extremely fine, cottony form of connective 

 tissue; the connective tissue unites those nerves which pass 

 most directly from the cerebral, pleural, and pedal ganglia to 

 the body wall, and thus a small space surrounding t?ie pharynx 

 is almost completely separated from the large body haemoccel. 

 The various ganglia are large, but not all distinct without care- 

 ful dissection because of their close fusion. Ganglia and nerves 

 are covered by thick connective-tissue sheaths. The cerebral 

 ganglia (fig. 33, Plate VI) are fused into a single mass which 

 shows no median constriction or other sign of its double origin. 

 The optic and rhinophoral nerves arise from its dorsal surface; 

 nerves to the other parts of the head spring from the anterior 

 margin. The cerebro-pleural and cerebro-pedal connectives are 

 either separated by a slit, or are so loosely united by connective 

 tissue that they can be easily distinguished. The pleural and 

 pedal ganglia of each side are closely fused. The pedal com- 

 missure is large, and a narrow parapedal commissure is also 

 present upon the posterior face of the pedal commissure; these 

 two may be separated by a narrow space toward the right side. 

 The visceral and parietal ganglia are closely fused to each 

 other and to the right pleural ganglion, but are connected to the 

 left pleural ganglion by a long and fairly thick pleuro-visceral 

 connective. The cerebro-buccal connectives arise from the sides 

 of the cerebral ganglia, just in front of the roots of the cerebro- 

 pedal connectives. They make an unusually wide loop around 

 the sides of the oesophagus and join the sides of the buccal 

 ganglia instead of the posterior surfaces, as is more commonly 



