568 F. W. C4AMBLE AND J. H. ASHWORTH. 



otocyst. The otocyst of A. Grubii agrees in all essentials with this one. 

 X 200. 



Fig. 65. — Section across the otocyst of a specimen of A. cristata from 

 Naples (300 mm. long). The distinction between the sensory and supporting 

 elements (Sens. C. and Sup. C.) is clearly shown. Note the single large 

 chitinoid otolith, x liO. 



Tig. 66. — Horizontal section of a giant-fibre of A. Grubii, to show the 

 outer sheath of ueurilemna (Nllm.), the true neuroglial sheath {fff. sh.), and 

 an inner myelin sheath {My. S/i.) which is dissolved out in the specimen figured. 

 The contents of the fibre consist of very delicate fibrillse in a faintly staining 

 protoplasm. X 500. 



PLATE 28. 



All the drawings of this plate are taken from a specimen of Arenicola 

 Grubii 78 mm. long. 



Figs. 67 — 70. — These are four camera drawings of consecutive sections 

 through a giant-cell, its process, and the point of union of this process with a 

 lateral giant-fibre. In Fig. 70 the structure of the process and cell are well 

 shown, particularly the neuro-fibrillse {Nllts.). In the giant-cell the neuro- 

 glial network and outer alveolar layer should be compared with the enlarged 

 figures, 76 and 77. The branch of the cell-process to the fibrous part of the 

 cord is seen in Fig. 69 {G. c. proc.fb.). 



Corrosive acetic, iron-haematoxylin. Outline of the figure drawn with oc. 6, 

 obj. D of the Zeiss system, and the detail under Zeiss oil-immersion apochro- 

 matic objective with an aperture of '02 mm. x 350. 



Figs. 71—73. — Three consecutive sections to show the connection between 

 the giant-cell and the median giant-fibre in segment 5. The alveolar structure 

 of the cell protoplasm and the ueuro-fibrillee of the cell process {Nll(S.) are 

 distinct. X 350. 



Fig. 74. — Transverse section of the cord in segment 8 to show the fusion of 

 the two lateral with the median giant-fibre and the branch from this union to 

 the spinal nerve on each side. On the left side the branch is prolonged in 

 the section to the base of the spinal nerve, x 350. 



Fig. 75. — Longitudinal section of the nerve-cord just behind the sixteenth 

 ueuropodiuin. Two giant-cells are seen surrounded by ordinary ganglion 

 cells. Each giant-cell has a neuroglial sheath {Ngl. Sh.), and the process of 

 each to the cord is cut off transversely {G. c. proc). The neuroglial fibrillse 

 are chiefly confined to the median line. The network in the giant-cell is 

 neuroglial in nature. X 380. 



Figs. 76 and 77. — Consecutive sections of the body of a giant-cell of the 

 same specimen of A. Grubii, to show the minute structure. The outer 



