14 THE CHICAGO ACADEMY OF SCIENCES. 



minor nerve centers such as the BUCCAL GANGLIA, OSPHRADIUM, etc. All 

 but the abdominal ganglion are paired. These ganglia, with their 

 nerves and commissures, may be briefly described as follows : 



The CEREBRAL GANGLIA (1) are situated above or a little to the 

 side of the oesophagus and are joined to each other, to the pedal gan- 

 glia and to the pleural ganglia by short, thick commissures. These 

 ganglia are made up of a number of small lobes, each of which is 

 probably the center for some particular nervous direction. The right 

 cerebral ganglion sends a nerve to the male generative organ which 

 divides before reaching that organ, one branch going to the penis (15) 

 and the other, which again subdivides, innervating the penis-sac (14). 

 The cerebral ganglia also send nerves to the tentacles (12), optic 

 nerves to eyes (10, 11), nerves to the front of the head (9), labial 

 nerves to the region of the mouth (17) and a pair of nerves to the 

 buccal sac. These latter or cerebral commissures enlarge on the buccal 

 sac to form the buccal or stomato-gastric ganglia. A small nerve (13) 

 arises from the posterior lobe of the right cerebral ganglion and in- 

 nervates the region of the neck. Two nerves (32) supply the labial 

 arteries. These ganglia also send out a number of small nerves which 

 innervate the buccal sac and the manducatory organs. Branches are 

 also sent to the salivary glands. 



The PEDAL GANGLIA (7) are very large, lie directly beneath the 

 oesophagus, and are connected with the cerebral and pleural ganglia 

 by short, thick commissures. These ganglia send off two sets of 

 nerves of three each, the first, inferior and superior cervical and colu- 

 mellar nerves (16, 18, 19, 26, 27) to the posterior part, and the second, 

 superior, inferior and central pedal nerves (28, 29, 30) to the anterior 

 part of the foot. There are several other short, minute nerves in- 

 nervating the fore part of the body. The otocysts (31) are placed in 

 the posterior part of the pedal ganglia, and are connected with some 

 of the other ganglia by fine nerves. 



The PLEURAL GANGLIA (2, 6) lie below the oesophagus, and are 

 connected by short, thick commissures with the pedal, cerebral and 

 visceral ganglia. They apparently send off no nerve cords. 



The VISCERAL GANGLIA (3, 5) lie behind, and a little above the pleu- 

 ral ganglia, and are connected with the latter and the abdominal ganglia 

 by short commissures. The right ganglion sends off a long nerve (24, 

 right pallial nerve) which innervates the female genital orifice, a por- 

 tion of the respiratory cavity and the right posterior part of the 

 mouth. Near the end of this nerve an enlargement forms the olfac- 

 tory organ or osphradium (25). A shorter nerve (33, anterior pallial), 



