ANATOMY AND CLASSIFICATION OF THE ARENICOLIDJl. 487 



adverted to^ and the fibrils radiating into the onter layers of 

 the protoplasm of the giant-cell (PI. 28, fig. 76, Ngl.jilx.). In 

 one or two giant-cells the glia-fibrillse penetrate more deeply 

 into the protoplasm, and form a definite network, staining 

 deeply and sharply with iron hEematoxylin or Apathy's 

 htematein 1 a. 



The protoplasm itself presents certain peculiar appearances. 

 The outermost layer is distinctly alveolar,^ and is demarcated 

 on its inner surface by a distinct membrane, or what seems to 

 be such, and which in sections is seen to be traversed by pro- 

 cesses from the glia fibrillae of the sheath. The outer alve- 

 olar layer is clear, non-granular, and does not stain. At each 

 end of the cell is a distinct vacuole, which has also been 

 noticed in the giant-cells of other annelids. The rest of the 

 cell protoplasm can be differentiated into (1) the main body 

 of the cell; and (2) one, or in some cells two regions, which 

 have characters similar to those described for the centro- 

 spheresof the giant-cells of Maldanids by Miss Lewis (1898), 

 and also resembling to a certain extent the description of 

 centrospheres in the ganglion cells of leeches and of Lumbri- 

 cus as given by Apathy (1897). The main mass of the cell- 

 protoplasm stains lightly. It contains a multitude of minute 

 granules, and these are often arranged as a network round 

 or in, a clear non-staining substance, thus giving a character- 

 istic " Wabenstructur." Different giant-cells vary much in 

 this respect, however; some, as in PI. 28, figs. 70, 7(3, showing 

 it very clearly, while others show a uniformly granular sub- 

 stance without alveoli. Should the alveolar structure occur, 

 it is usually very plainly marked round the nuclear membrane, 

 and may extend up to the membrane noted already. With 

 reference to the so-called centrospheres we may mention the 

 radiating arrangement of chromophilous granules round a 

 central point, usually between the excentrically placed nucleus 



1 The whole question of the existence of alveoli and fibrils in living cells 

 has lately been reopened. See the very suggestive paper by W. B. Hardy 

 in the 'Journal of Physiology,' vol. xxvii, 1899, "On the Structure of Cel^ 

 Protoplasm." 



