200 DR. J. S. BOWERBANK ON Sl'ONGIAD^E. [Feb. JO, 



The orifices to the open pores in the dermal membrane varied in 

 diameter from ^|-j inch to y^Vir i ucn - Immediately beneath the 

 dermal membrane there is a stratum of sarcode filled with minute 

 cvlindro-stellate spicula. This stratum forms about two fifths of 

 the entire thickness of the dermal crust, which is connected with 

 the mass of gemmules beneath by the fusiformi-acerate spicula of 

 the dermal crust. The distal points of these spicula pass through 

 the dermal membrane, while their proximal ones are embedded in 

 the outer surface of the ovarian stratum, which forms about three 

 fifths of the entire thickness of the crust. 



The stratum of sarcode filled with minute cylindro-stellate spicula 

 appears to perform a very important part in the economy of the 

 animal. It is traversed by minute canals at various angles, each 

 canal being connected at one end with a pore, and terminating at 

 the other in the expanded distal extremity of an intermarginal 

 cavitv. The cylindo-stellate spicula, strengthening and supporting 

 the sarcode stratum, are exceedingly minute ; they vary in their 

 extreme diameter from -^j^j to -g-gVe" ^ ncn - The length of the fusi- 

 formi-acerate spicula is ^ inch. 



The arrangement of the ternate connecting spicula at the inner 

 surface of the crustular coat is exceedingly interesting : they occur 

 in a series of bundles ; the long attenuated shafts of each fasciculus 

 approximate at their bases and diverge thence until the ternate head 

 of each is about equally distant from its surrounding neighbours ; 

 and the extremities of the rays touch or slightly cross each other, 

 thus forming a beautiful regular angular network, the meshes being 

 six or seven-sided according to circumstances. The upper surfaces 

 of the radii are firmly attached to, or partially embedded in, the 

 under surface of the crustular stratum. Within each of these areas 

 there is usually to be seen the proximal end of one of the intermar- 

 ginal cavities. 



The intermarginal cavities exhibit a high degree of organization ; 

 they are in form not unlike a bell, the proximal end being at the 

 inner surface of the crustular dermis, and the distal one at the inner 

 surface of the stratum of sarcode and stellate spicula immediately 

 beneath the dermal membrane, and towards which it gradually in- 

 creases in its diameter ; the proximal end of one measured -^J-g inch 

 in diameter, and the distal end -pl^ inch. These cavities are lined 

 throughout their length with a stout transparent membrane ; and at 

 the proximal end of each cavity there is a strong membranous dia- 

 phragm, which in the greater number of cases was in a closed state ; 

 in this condition the membrane was filled with concentric circles 

 composed of minute rugae or thickened lines, and at the centre was 

 closely pursed together, completely closing the orifice. In some the 

 membrane was only partially closed, and the orifice was either cir- 

 cular or slightly oval ; and in two instances in the same field of view 

 the orifices were nearly as large as the basal opening of the bell- 

 shaped cavity, and the central margin of each diaphragm at its 

 proximal end was dense, highly coloured, and much thicker than at 

 the other parts of the membranes. The pursing of the membrane 



