18 EHIZOPODA. 



If the circular flattened disk of one of these fonns 

 {fig. 4, a) be submitted to microscopic examina- 

 tion, a series of rounded elevations disposed in 

 concentric annular bands round a central " nu- 

 cleus " may be observed on its surface, whilst its 

 margin is seen to consist of an undulating succes- 

 sion of rounded projections alternating with de- 

 pressions, each of the latter being provided with 

 a single orifice. On more careful examination, 

 we find that each of the rounded elevations con- 

 stitutes the upper surface of a chamber or cell, 

 *' which communicates by means of a lateral 

 passage with the cavity on either side of it in the 

 same ring ; so that each circular zone of cells might 

 be described as a continuous annular passage, 

 dilated into cavities at intervals. On the other 

 hand, each zone communicates with the zones 

 that are internal and external to it, by means of 

 passages in a radiating direction ; and it is curious 

 that these passages run, not from the cells of the 

 inner zone to those of the outer ; but from the con- 

 necting passages of the former to the cells of the 

 latter ; so that the cells of each zone alternate in 

 position with those of the zones that are internal 

 and external to it. The radial passages from the 

 outermost annulus make their way at once to 

 the margin, where they terminate, forming the 

 * pores ' which (as already mentioned) are to be 

 seen on its exterior. The central nucleus, when 

 rendered sufficiently transparent (by previous pre- 

 paration), is found to consist of a central cell {v\ 

 usually somewhat pear-shaped, that communicates 

 by a narrow passage mth a much larger circum- 

 ambient cell (tt), which nearly surrounds it, and 

 which sends off a variable number of radiating 



