THE ANATOMY OF SCALIBREGMA INFLATUM. 309 



Fig. 21. — A very small nephridium drawn in situ on the body-wall after 

 the preparation had been stained and cleared. Note the septum accompany, 

 ing the blood-vessel to the nephrostome. On the right of the nephrostome 

 the nuclei of genital cells are seen. The excretory part of the nephridium^ 

 the loop — is at this stage very short. The nephridium is closely invested by 

 a delicate coelomic epithelium, the nuclei of which are seen at intervals. 

 X 300. 



Fig. 22. — Section of an ovum from a specimen 35 mm. long. The peri- 

 pheral layer of protoplasm is almost free from yolk granules, x 150. 



Fig. 23. — Section of a portion of the wall of the (Esophageal pouches, to 

 show the blood-sinus enclosed between two epithelial lamellae, x 50. 



Fig. 24.— Some of the cells of the wall, showing the cavities iu which the 

 granules of secretion are usually found. They have been dissolved from these 

 cells leaving the cavities empty, x 300. 



PLATE 15. 



Fig. 25. — Two furcate seta;. A in full view ; B in profile. The portion 

 shown in the figure represents only the distal twelfth of each seta, x 800. 



Fig. 26. — The tip of a capillary seta, to show the hair-like processes. The 

 portion figured is only -^-^ of the seta. X 800. 



Fig. 27. — Section of a very young sense organ. The organ was situated 

 •25 nun. from the posterior end of a specimen 13 mm. long. There was only 

 one chsetigerous segment behind this one, and in both these segments the 

 notopodia! setae only were formed, as shown. This is the earliest recognisable 

 sense organ in the specimen. Note the minute rods {R.), the three ganglion 

 cells, and the nuclei of the multipolar ganglion cells {N. M. C), For further 

 explanation see p. 274. X GOO. 



Fig. 28. — A rather thick longitudinal section of a sense organ about 3 mm. 

 from the posterior end of the specimen 13 mm. long. The sense-hairs are 

 now seen. This sense organ contains an exceptional number of large ganglion 

 cells. X 500. 



Fig. 2'J. — Transverse section of a parapodium of the same specimen 

 situated 2 mm. from the posterior end. The retractor muscle of the sense 

 organ is seen. See also p. 272. x 500. 



Fig. 30. — Transverse section of an old sense organ from the twenty-fifth 

 segment of a specimen 35 mm. long. The fibrous part of the organ is pro- 

 portionately larger. The ganglion cells are situated nearer to the rods in this 

 organ than in most others. Note the stout nerve supplying the organ enter- 

 ing on the ventral side, and turning almost through a right angle into the axis 

 Qf the organ. See p. 274. X 200. 



