ANATOMY AND CLASSIFICATION OF THE ARENICOLID.E. 567 



anterior end of the melastomial groove. The circumcesophageal nerve- 

 connectives and their point of union are shown by dotted lines. Tiie four 

 Cttlomic spaces are portions of a continuous anterior extension of the ccelom. 

 The figure has been constructed from sections cut in three planes. X 100. 



Fig. 57.— a slightly oblique section across the middle of the brain of A. 

 Claparedii (26 mm. long), to show the great development of neuropile 

 {Npile.), tlie neuroglial cells {Nrgl.), and the sensory elements of the prostomial 

 epithelium (^Prost. Epith.). In the braiu the ganglion cells of the middle 

 cerebral lobes {Mid. gang.) form two lateral masses separated by a median 

 coelomic space. Cam. luc. X 110. 



Fig. 58. — Transverse section across the prostomium of the same specimen 

 A. Claparedii, cutting the extreme ends of the anterior cerebral lobes. The 

 neuropile is dotted. Cam. luc. X 110. 



Fig. 59. — Anterior end of an adult specimen of A. Claparedii from 

 Crescent City, California, seen from above to show the form of the prostomium. 

 X 8. 

 Fig. 60. — The same seen from the side. 



Fig. 61.— Anterior end of a young specimen (15 mm. long) of A. 

 Claparedii from Naples, seen from above to show the higlily developed 

 prostomium. x 18. 



Fig. 62.— The same from the side, x 20. 



Fig. 63. — Horizontal section of the brain and prostomium of A. marina, 

 from a specimen 60 mm. long. The neuropile is dotted. The commissure 

 {3Iid. Cotiim.) which binds the anterior lobes together is cut horizontally. 

 The arrangement of the large pyriform ganglionic cells {Ant. gang.) round the 

 coelomic spaces is very evident. The nuchal groove {Nuc. Gr.) is cut across 

 obliquely. X 75. 



Fig. 63 a. — Part of a transverse section of the prostomium of Arenicola 

 ecaudata, to show the eyes embedded in the nervous tissue underlying the 

 epidermis. The latter is composed at tiiis point of mucus-forming cells 

 {EpUh. sec), broader at their outer ends than at their inner ones. The rest of 

 the thickness of the section is made up of a nervous tissue composed of cells 

 (the nuclei of which are seen at n. n.) and wavy fibres. The lens-like body 

 and the pigment granules of the eyes are well seen. n. form refers to a 

 nucleated mass which is probably the cell in which the eye has been formed. 

 X 440. 



Fig. 64. — Section across the otocyst of a full-grown specimen of A. 

 ecaudata. The outer layer is composed of connective tissue supportintr a 

 nerve-sheath {N. Sh.) whicli results from the branches of the otocyst nerve 

 {Ot. N.). The sensory epithelium contains supporting cells, whicli, however, 

 are not distinguishable in this figure. In the centre of the organ are the 

 chitinoid otoliths, which have been drawn from a whole preparation of the 



