EXPIvANATlON OF PIRATE XXI. 



Fig, I. Investigator sicarius, x 6. 



,, 2. Spine from trunk, highly magnified. 



,, 3. Spine from edge of shield, highly magnified. 



,, 4. The gill and gill-chamber. The shield has been split in two longitu- 

 dinally in the sagittal plane. The cut surface of one half is represen- 

 ted, showing one half of the gill lying in the gill-chamber, x 10. 



,, 5. Transverse section through the neck, to show structure of body-wall, 

 the division of the cœlom by the coronal diaphragm and the position 

 of the lateral nerve cords, x 80. 



,, 6. Transverse section through the commencement of the trunk. Shows 

 the cœlom at its greatest extension with four septa in addition to the 

 coronal diaphragm, x 60. 



,, 7. Transverse section through trunk, x 35. 



,, 8. Transverse section through hind end of the trunk at the level of the 

 • anterior wall of the respiratory chamber, to show the union of the 

 lateral nerve cords in the posterior nerve commissure dorsal to the 

 alimentary canal, x 37 : siph. is a siphon-like outgrowth of the hind- 

 gut. The section of the alimentary canal in the dorsal region of the 

 figure is an oblique longitudinal section. 

 The longitudinal nerves are too minute in this section to appear in the 

 drawing. 



,, 9. Transverse section through the shield, x 55. 



Reference i^ETTERS. — a.b.v. = dorsal blood-vessel ; al.c. = alimentary canal ; 

 cart. = cartilage ; ce. = cutting edge ; e.g. = cerebral ganglion ; chit. = chitinous 

 cap ; cm. = circular muscle ; coel.c. = cœlomic corpuscles ; cor.d. = coronal dia- 

 phragm ; ep. = epidermis ; gi. = gill ; gl.ap. = aperture of poison gland ; /. = liver ; 

 l.m. = longitudinal muscle ; n.c. = lateral nerve cord ; neph. = nephridium ; p. gl. — 

 poison gland ; ph.gl. = pharyngeal gland ; p. n.c. = posterior nerve commissure ; 

 r.c.n. = recurrent portions cf lateral nerves on the respiratory chamber; resp.ap.= 

 aperture of respiratory chamber ; resp.c. = wall of respiratory chamber ; resp.cav. = 

 respiratory cavity; resp.lam. = respiratory laminae of gill-chamber; s. = septum; 

 t. = testis. 



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