76 Invertebrate Zoology. 



Follow the oviduct far back and note the abrupt turn in 

 its course as it bends anteriorly. Trace it to its opening 

 into the capsule of the ovary. The ovary lies along the 

 dorsum and extends anteriorly from near the posterior end 

 of the animal to a point dorsal to the external opening of 

 the oviduct. In its substance are to be seen the eggs or ova, 

 in varying stages of maturation. 



The Excretory System. The cavities and the external 

 openings of the nephridia have already been noted. Such 

 glandular tissue as is present is concentrated along the sides 

 of the venae cavae. 



The Nervous System. - - Observe on each side of the 

 animal, at a point on the inner surface of the mantle just 

 anterior to the attachment of the retractors of the head, the 

 large stellate ganglia. From these ganglia radiating nerves 

 may be traced to different portions of the mantle and, run- 

 ning anteriorly from each, through the retractor of the same 

 side, and thence to the infra- ozsophageal ganglion, are the 

 rig/if and the left pleural nerves. Carefully trace these 

 nerves to the cartilaginous support of the head, and then 

 remove the tissue from the ventral side of the eyes until the 

 enormous optic ganglia are exposed. 



Lying ventrally, between the optic ganglia, and protected 

 by cartilage, are the fused pedal, pleural, and visceral ganglia. 

 They form the infra-cesophageal mass. 



With a sharp scalpel carefully slice away the ventral carti- 

 lage, exposing the deep-lying nervous mass. Note, as the 

 cartilage is being removed, the central cavities or auditory 

 chambers. 



The infra-cesophageal mass is prolonged anteriorly into 

 the pro-pedal ganglia, which give rise to ten radiating 



