Chap. III. GENUS PLEUROBRACIIIA. 219 



the peri^^beric side ; but the wall is continuous with the outer wall (page 235, Fig. 

 87 (>' ()") of the tentacular apparatus, and thus the circle is completed. 



The next system that demands our consideration is the largest of all; and we 

 may call it the radial system, from the fact that it radiates equally on all sides, 

 from the digestive cavity and the axial funnel to the peripheric systems. When 

 seen from the actinal {Fig. 21) or abactinal pole, the cells seem to radiate in direct 

 lines from an imaginary centre ; but in a profile view {Fig. 2.3), the true course 

 of these bodies {nv' t t^) is discovered to be in two oblique directions, one of which, 

 radiating from the digestive cavity {h c), recedes from the actinal toward the oppo- 

 site pole, and the other, radiating from the axial funnel (/), is inflected toward the 

 digestive cavity as it passes on to the periphery. Besides the general direction 

 of these two courses, there is another peculiarity which is quite remarkable : the 

 axis of each cell, instead of being a straight line, is curved {Fig. 24) ; so that the 

 main trend of these bodies does not recede in a direct course from the two polar 

 ends of the body, but in long arches. The degree of flexure in these two courses 

 varies in different parts of the body, and may be most appropriately described 

 in connection with the details of this system, to which we now proceed. The 

 shortest span which the radial system makes, lies Ijetween the corners of the mouth 

 {Fig. 21 «^) and digestive cavity, and those bands of the interambulaci-al system 

 which are in the plane of the latter organ, and therefore at right angles to the 

 plane which passes through the tentacular sockets (/) and the two chymiferous 

 tubes (r r) on each side of the digestive cavity. In this region the cells pass 

 to the periphery in a course which recedes but little from the mouth, and which 

 curves very slightly toward the centre of the body. In the same plane, at the 

 opposite pole, the span is longer, on account of the smaller dimensions of the axial 

 funnel {Fig. 23 /), but the trend of the cells is about the same : in fact, they have 

 the same trend and curve as at right angles to this plane {Fig. 23 t i}) and at 

 all intermediate angles. 



But, to return to the actinal pole, we would remark that we find the trend 

 of the radial system {Fig. 21 m ir?) very much modified as we trace it through 

 ninety degrees from the plane of the digestive cavity ; for the recession becomes 

 gradually more noticeable, vmtil it reaches its maximum in the region where {Fig. 23 

 m-) the cells pass to the tentacidar sockets (/) with a trend of forty-five degrees 

 to the axis of the body. The sj^an, which is so short oj^posite the corners of 

 the mouth and digestive cavity, gradually increases in length, until it attains to 

 the longest reach in passing to the chymiferous tubes {V- P and l^ l^) which embrace 

 the tentacular sockets (/) ; and then the latter, by obstructing the way, suddenly 

 shorten it by more than one half 



This will be more fully comprehended as we now proceed to describe the several 



