20 W. BLAXLAND BENHAM. 



Fig. 8. Copied from Boveri's fig. 14, pi. xxxiii. "Transverse section 

 of tongue bar at the level of the nephridium. neph. Position of nephri- 

 dium. vi 11 . Inner axial vessel. ve n . Outer axial vessel." 

 Fig. 9. Copied from Schneider, pi. xiv, fig. 3. "Transverse section of 

 a thick (i. e. primary) gill bar. A 1 , A^. Blood-vessels which are in 

 communication with the branchial artery, a. Triangular space, blood- 

 vessel, p. p. Peritoneal (i.e. atrial) plate. V. Vein in communication 

 with the subvertebral vein, and the venous space around the branchial 

 artery. 2 . The thick rod." 



Fig. 10. Copied from Lankester, pi. xxxvi B, fig. 1. " Transverse 

 section of a primary bar. B.v. Blood-vessel connected with the lateral 

 branches of the median endostylar vessel, fas. Fissure due to the 

 bilateral origin of the rod. cos. ep. Ccelomic epithelium, pg. Pigmented 

 atrial epithelium." 



Fig. 11. Copied from Spengel's fig. 12, pi. xvii. "Outer part of a 

 transverse section through a primary bar. b. m. Basal membrane. 

 cbk. Coelomic canal of the bar. sp. Skeletal rod. vk. Chief vessel in 

 the primary bar." 



Fig. 12. Copied from Boveri, fig. 6, pi. xxxii. " Transverse section of 

 a primary gill bar, vi 1 . Inner axial vessel. ve l . Outer axial vessel. 

 vc. Coelomic vessel, coe. Ccelom." 



FIG. 13. A tongue rod in section, to show the skeletal blood-vessel (sk. b. 

 v.} running in a special canal ; it is probably about to anastomose with the 

 somatic vessel (som. b. v.}. Around the ccelom (ccel.) three nuclei (n. c. ep.} 

 are present, embedded in granulations (? protoplasm). In this section the 

 two blood-vessels, as is frequently the case in cochineal preparations, are 

 stained deep red. The ccelom is quite clear, cu. cutis. 



FIG. 14. A rod from a tongue bar, exhibiting granulations in the cavity, 

 which are of two kinds : a coarser, less deeply stained, in the outer part, which 

 is probably the protoplasm of coelomic epithelium in that region marked 

 coe. coelom ; and a finer and more deeply staining mass (skel. b. v.), the 

 skeletal blood-vessel. The two are apparently separated by a partition. 

 n. is the nucleus of the ccelomic epithelium, som. 6. v. The outer or somatic 

 blood-vessel, cu. The " cutis" or outer wall of coelom. From a preparation 

 stained with Mayer's alcoholic cochineal. Drawn under Zeiss's homogeneous 

 immersion. 



FIG. 15. A modification in the shape of the section of the rod, which is 

 not unusual, especially near the synapticula. The rod is here composed of 

 two pieces. The outer wall of the coelom is free of skeletal tissue (cf. Fig. 

 31), and the blood-vessel (skel. b. v.} is passing out of the coelom (ccel.), and 

 lies just below the atrial epithelium (at. ep.). 



FIG. 16. Another modification in the tongue bar, which occurs near the 

 upper end of a bar. 



