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

 vessel through the inter-filamentar junctions to supply the 

 filaments. The vessel bv' is the vessel into which the blood 

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

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

 severity diameters. 



PLATE 10. 

 FIG. iS. 1 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. icy. Section* of an animal taken through the plane that connects the 



cartilage,, anid 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 seeji -f rpm the ventral side. These may easily 



r I i'i* be exposed for study ,]?y stripping the .thin muscular covering 



fronr 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-. .. j . , j ,. 



