DIVISION OF COLLAR-CELLS OF CLATHRINA COEIACEA. 621 



tracted, tlie collar-cells become taller and narrower and the 

 collar much shorter. In each cell the basal three fourths of 

 the body is broader and more or less cylindrical in shape ; 

 this part of the cell is in contact with the neighbouring cells, 

 and constitutes the main body of the cell. We have not found 

 processes connecting the bodies of the cells with one another. 

 It has been shown by Minchin and Reid (14) that when the 

 collar-cells are carefully brushed away and the wall of the 

 sponge is stained with picro-nigrosin, a delicate blue-stained 

 network is visible in surface view, representing a honeycomb- 

 like structure, the spaces in which were originally occupied 

 by the bodies of the collar-cells. Hence in life the bodies of 

 the collai"-cells are probably not in actual contact, but are 

 separated by a delicate extension of the gelatinous ground- 

 substance of the body-wall of the sponge. If, as would seem 

 probable on theoretical grounds, the bodies of the collar-cells 

 are connected across this intervening substance by proto- 

 plasmic fibrils, such connections have escaped our notice, 

 possibly on account of their being of extreme tenuity and 

 requiring, perhaps, other methods of technique, in order to 

 demonstrate their existence, than those employed by us for 

 the study of the mitosis. It is well known that in other 

 sponges the collar-cells may be connected by protoplasmic 

 processes, as, for instance, in Hexactinellids, where such 

 processes are extremely obvious, forming the so-called 

 mem br ana reticularis. 



The cylindrical basal portion of the cell ends in a distinct 

 rim or flange, and from this level arises a narrower portion, 

 which may be termed the " neck," and which is quite free 

 from any contact with neighbouring cells. The summit of 

 the neck is rounded off, formingf a convex lens-like area 

 enclosed by the base of the collai-, and giving off centrally 

 the flagellum. The so-called collar has more the form of a 

 cuff or sleeve when fully expanded. It is distinctly thicker 

 and more rigid in its basal portion, becoming very delicate at 

 its distal end, which is usually more or less shrunk and dis- 

 torted in preparations. The uppermost limit of the collar is 



