308 J, H. ASHWORTH. 



cesopliageal pouches, the vascular system and tlie nephridia (see also p. 254). 

 The neuropodia and the afferent nephridial vessels are drawn only in the five 

 segments immediately behind the last diaphragm, and the oblique muscles, 

 which are present in all the chaetigerous segments, are shown only in the last 

 three segments drawn on the right side. The incomplete ventral mesentery, 

 which binds the ventral wall of the stomach to the body-wall near tiie nerve- 

 cord, is omitted. In order to prevent confusion, the course of the blood- 

 vessels running on the left side of the body-wall is not fully shown behind 

 segment 15. Some of the folds in the wall of the stomach are probably arti- 

 ficial. X 3. 



Pig. 15. — A section passing almost horizontally through the head, pro- 

 stomium, and first and second chaetigerous somites, to show the brain with its 

 anterior and posterior cornua lying in the proslomium, the nuchal organ, and 

 its retractor muscle, etc. The ganglion cells which cover the brain are in 

 close relation to the epithelium of the prostomium and of the nuchal organ. 

 The section has not passed through the whole length of the anterior lobe of 

 the brain, only its posterior portion is seen here. X 80. 



Fig. 16. — Transverse section of the specimen shown in Fig. 1 passing 

 through the twenty-fifth clisetigerous aunulus. The various parts of the 

 parapodium and the sense organ are seen on the right (cf. Fig. 9). In the 

 ventral divisions of the ccelom sections of the small tubular nephridia are 

 seen ; on the left a nephroslome has been cut through. At the base of the 

 ventral groove in the intestine are two cords {Int. N.) seen in section. From 

 their structure and general appearance they appear to be nervous, x 24. 



Fig. 17. — Transverse section of the nerve-cord and surrounding structures 

 from a specimen 14 mm. long. The fibrous part of the cord is partially sub- 

 divided by a neuroglial ingrowth. The ganglion cells are situated chiefly on 

 the ventral side of the cord. The origin of a spinal nerve is seen on the 

 right. Note also the nuclei of the longitudinal muscle-fibres. X 200. 



Fig. 18. — A nephridium from the twentieth segment of the specimen seen 

 in Fig. 1. The lumen of the nephridium is shown, as seen in optical section 

 Attached to the nephrostome is the rudimentary septum bearing the genital 

 cells. X 40. 



Fig. 19. — Section of a nephrostome from the thirtieth segment of the same 

 specimen. The dorsal lip is seen on the right, it is more strongly ciliated 

 than the ventral lip. On the left is the septum bearing the genital cells. 

 The blood-vessel lies between the ccelomic and the ciliated epithelium. 

 X 250. 



Fig. 20. — Section of a small nephridium at the junction of the excretory 

 and terminal portions. The latter is on the right; its cells are cubical or 

 even slightly flattened, while those of the excretory portion are columnar, 

 and have vacuoles which in life probably contained excretory products, 

 X 250, 



