406 W. H. GASKELL. 



6, 8, PI. XXV, and 20a— 20 d, PL XXVII. The body of 

 each cell contains a homogeneous semi-fluid substance, which 

 stains but slightly with osmic acid. In the centre of this 

 is seen in some cells an irregular brownish mass, in others 

 a more clearly defined large round nucleus, surrounded with 

 some of the same irregular brown granular-looking debris. 

 In other cells nothing is seen but the clear slightly-staining 

 fluid. These appearances evidently mean that the cells com- 

 posing this substance have so much thickness that some sections 

 pass through the nucleus ; others through the scanty granular 

 strands of material surrounding the nucleus, which represent 

 the remains of the protoplasm of the cell ; and others still nearer 

 the edge of the cell, where nothing but clear fluid is to be 

 found. The same appearances are seen in whatever direction 

 the section is made, showing that these cells are solid poly- 

 gonal bodies pressed together in all directions, without any 

 sign of being in connection with specially arranged connective- 

 tissue elements either in one direction or the other. Again, 

 that they have no connection with adipose tissue is evident, 

 for in the first place they do not stain like fat. A small fat- 

 globule may be seen here and there, but that is all. All the 

 deep blackness seen in the osmic preparations is due to the 

 presence of pigment in between the cells. In the second place, 

 the nucleus lies in its natural position in the centre of the cell, 

 and the semi-fluid contents lie simply in between the meshes 

 of the degenerated-looking protoplasmic material which sur- 

 rounds the nucleus and spreads thence towards the periphery. 

 Again, staining with hsematoxylin or carmine gives appear- 

 ances as drawn in fig. 15, PL XXVL Here, again, we see that 

 the nucleus stains but poorly, and the staining material in the cell 

 consists of a broken-down network whicli starts from the nucleus 

 and forms scanty strands which pass towards the periphery. 

 In fact, the structure and massing of this '' arachnoidale Fiill- 

 gewebe " is precisely what one would expect if it represented 

 the degenerated remains of the cephalic liver of the Crustacean- 

 like ancestor of the Ammocoetes. 



I have already described its general arrangement on the 



