822 DESCEIPTION OF PLATES. 



i.o. Infrabuccal organ (only the sheaths of the tentacles indicated on either side of the 

 organ of Owen). 



e.b. Extrabuccal lobe. 



c.e. Cut edge of buccal membrane. 



i.n. Infrabuccal nerve. 



n.f. Infundibular nerve. 



p.c. Coronal (pleuro-pedal) commissure. 



a.e. Arcus cartilaginis. 



i.r. Ventral retractor muscle. 



N.B. The actual distance between the roots of the infundibular nerves was 14 mm. ; 

 between the infundibular and infrabuccal nerves on each side, 4 mm. 



Fig. 5. Another dissection (N. pornpilius $) exposing the fundus of the peristomial 

 haemocoel ; the funnel and oval sheath (cephalopodium) have been sliced away and the buccal 

 cone turned back. 



Letters, commencing from left side of figure : — 



r.a. Recurrent tentacular artery. 



o.s. Orifice of ophthalmic sinus. 



c.s. Orifice of spadical sinus (a spacious reservoir surrounding the base of the spadix, 

 probably assisting, by blood-pressure, in the protrusion of the latter). 



i.n. Infrabuccal nerve. 



n.i. Infundibular nerve. 



a.i. Arcus cartilaginis. 



c.c. Coronal commissure. 



i.r. Ventral retractor. 



c.i. Cartilage. 



l.i. Levator infundibuli. 



e. Eye. 



h. Hood. 



Between a.c. and c.c. lies the passage leading from the peristomial haemocoel into the 

 endochondral sinus. 



Fig. 6. Dissection resembling that of PI. LXXXI. fig. 6, but carried further. The 

 ophthalmic sinus is cut open, the rhinophore pulled aside, and the otocyst turned back. 



a.o.t. Anterior ophthalmic tentacle. 



a.o.n. Anterior ophthalmic nerve. 



I. Hood-nerve. 



II. — VIII. Digital nerves. (Between II. and V. occurs the common root of III. and IV.) 



v. Visceral nerve-collar cut across. 



o. Otocyst, turned back to expose the massive coronal ganglion. 



o.g. Optic nerve-ganglion complex. 



p.o.n. Posterior ophthalmic nesve, taking a recurrent course in the wall of the ophthalmic 

 sinus, mediad of the optic ganglion (the posterior ophthalmic tentacle itself is quite concealed 

 behind the eye in this view except for the apex which happens to project forwards between 

 the eye and the hood). 



r. Rhinophore. 



e. Eye. 



