OF THE SPONGIAD^E. 181 



mastia there is no central axial column. I could not detect 

 interstitial membranes in any part of the space intervening 

 between the axial column and the dermis in C. pencil/us, 

 but the skeleton column is permeated by numerous inter- 

 stitial canals. 



The structure of the short pedestals passing from the axial 

 column to the inner surface of the dermis is different from 

 that of the axis ; the spicula composing them are parallel 

 to each other, and they are firmly packed together. The 

 bases of the pedestals arise from the surface and from within 

 the substance of the central column, with which they appear 

 to have no further connection than that which is necessary 

 to secure them firmly in their respective positions. Their 

 apices present a very beautiful appearance, spreading out 

 towards the inner surface of the dermis in curves, in the 

 direction of angles of about 45 degrees, diverging in every 

 direction over its inner surface, which, when viewed with a 

 microscopic power of about 100 linear, resembles an elabo- 

 rately and beautifully groined roof of a Gothic crypt where 

 the pedestals impinge. 



Fig. 360, Plate XXX, represents a longitudinal section 

 through the central axis of one of the elongate cloacal 

 portions of the sponge, exhibiting the central column and 

 the small cylindrical pedestals or short fasciculi of closely 

 packed spicula, each terminating at the outer surface of the 

 dermis of the sponge, natural size. Tig. 361, exhibits a 

 section of the specimen represented by Fig. 360, at about 

 the middle of the cloacal column, showing the mode of the 

 radiation of the distal ends of the small pedestals on the 

 inner surface of the dermis, X 25 linear. 



TETHEA, Lamarck. 



. The following are the generic characters given by 

 Lamarck, in his ' Anim. sans Vert.' 2nd edit. ii. 384 : 



