ANATOMY AND CLASSIFICATION OF THE AflENICOLlDyE. 561 



I'lG. 23 b. — A portion of the same seta from the region marked +. 

 X 1000. 



Fig. 24. — A. Claparedii. The ventral portion of a iieuropodium of a 

 Neapolitan specimen 95 mm. long, showing the stages in the development of 

 the cliEetse. X 180. 



Fig. 25. — A. Claparedii. A neuropodial chseta from a Neapolitan 

 specimen 75 mm. long, to show the great curvature of the chseta. X 180. 



PLATE 24. 



Fig. 26. — Dissection of a specimen of Arenieola Claparedii from 

 Naples, to show the general characters of tlie internal anatomy. Tiie special 

 features shown are the three anterior diaphragms, the caudal septa, the 

 alimentary canal and the oesophageal pouches, the vascular system, and the 

 nepliridia. The vessels of the posterior portion of the alimentary canal are 

 more highly developed than usual in this specimen. The oblique muscles and 

 longitudinal muscle-bands are not shown. X 2. 



Fig. 27. — A portion of the oesophagus of a specimen of A. Claparedii 

 from Naples, showing the multiple oesophageal pouches. X 4. 



Fig. 28. — A portion of the oesophagus of a specimen of A. Claparedii 

 from Crescent City, California. In this specimen fifteen oesophageal pouches 

 are present, x 3. 



Fig. 29. — The fourth right nephridium of a Neapolitan specimen of A. 

 Claparedii, seen from the dorsal aspect, showing the dorsal lip of the 

 nephrostome {Nphm. D.) with its spatulate ciliated vascular processes, the 

 secreting portion of the nephridium (Np/i.), and the bladder (BL). Note also 

 the blood-vessels, the gonad {Oon.) upon the gonidial vessel {G. V.), and the 

 bluntly ending filamentous branches of the gonidial vessel. X 16. 



Fig. 30. — Dissection of the large specimen of Arenieola cristata from 

 the Harvard Museum, to show the general characters of the internal anatomy. 

 The special features shown are the three anterior diaphragms, the caudal septa, 

 the muscles, the alimentary canal, the vascular system, and nephridia. A 

 complete (seventh) nephridium is present on the right side in addition to the 

 normal six pairs, 'i'lie position of the first gill is clearly indicated by the 

 appearance on segment 7 {Not. SJ) of both afferent and efferent branchial 

 vessels {£r. Aff}, Br. Bff.^). The cirriform processes (C. P.) on the tail are 

 seen to be segmentally arranged. Natural size. 



This figure is to be compared with the similar dissection of A. marina 

 (Gamble and Ashworth, 1898, PI. 2). 



Fig. 31. — The posterior branchial and anterior caudal region of the same 

 specimen of A. cristata, seen from the right side, to show the last fully 

 developed gill {Br."^, the branches of which are cut short), the presence of a 

 rudimentary gill {Rud. Br.) on the first caudal segment, and the cirrifurm pro- 



