filament as the vessel ba". Branches are given oflf from this 

 vessel through the inter-filamentar junctions to supply the 

 filaments. The vessel bv' is the vessel into v^rhich the blood 

 that has traversed the gill is collected. It in turn communi- 

 cates with the vein of the gill (bv., Fig. ll). Magnified about 

 seventy diameters. 



PLATE 10. 

 Fig. i8. — Vertical section (from the suspensory membrane to the free 



edge) of a gill. Taken next to an inter-lamellar junction. 



Magnified about fifteen diameters. 

 Fig. 19. — Section of an animal taken through the plane that connects the 



cartilage and the visceral ganglia. Two-thirds natural size. 

 Fig. 20. — Section of an animal taken through the plane that connects the 



heart and the outer ends of the excretory organs. Two-thirds 



natural size. 



PLATE II. 



Fig. 21. — Transverse section of a modified filament (with the attached 

 portion of an inter-lamellar junction) and of two adjacent 

 filaments. The section is taken near the suspensory mem- 

 brane. Magnified about six hundred diameters. 



Fig. 22. — Transverse section of a sense tentacle of a young specimen. 

 Magnified about one hundred sixty-five diameters. 



PLATE 12. 

 Fig. 23. — Nervous system as seen from in front and a little to one side. 

 Natural size. (Diagramatic.) 



PLATE 13. 



Fig. 24. — Cerebral and pedal ganglia with their nervous connections, as 

 seen from the antero-ventral position. These ganglia and the 

 otocysts lie in a mass of connective tissue and may be dis- 

 sected out and mounted for study without injury. Magnified 

 about fifteen diameters. 



Fig. 25. — Visceral ganglia seen from the ventral side. These may easily 

 be exposed for study by stripping the thin muscular covering 

 from their ventral surfaces. They are hard to separate from 

 the adductor muscle but they may be mounted with a thin 

 piece of the muscle and studied in position. Magnified about 

 fifteen diameters. 



70 



