30 



The upper wall of this section, which thus forms properly the bottom of the digestive cavity, 

 and can also be seen more or less completely through the gaping bucal aperture (see Tab. 1, 

 fig. 2, 5 f) has the form of a flat extended circular disc of half the diameter of the proper 

 stomach. Its structure seems to be very peculiar. On the interior or lower side turned to- 

 wards the digestive cavity, it exhibits (see Tab. II, fig. 10) an appearance of being, as it 

 were, gi-anulated, having on its surface numerous small wart-like elevations or sinuosities 

 of a glandular structure, which, especially towards the centre, are crowded together and 

 projecting, and in this part frequently arranged in larger or smaller groups separated by 

 more or less distinct sinuous furrows; towards the periphery these elevations become more 

 indistinct, and disappear at last entirely where the radial caeca take their issue. The upper 

 side (see Tab. II, fig. 8 c) which is in great part covered by a glandular apparatus (f) at- 

 tached here in the centre, (hereafter more particularly noticed) seems to exhibit an entirely 

 ditfereut structure. We remark here a very conspicuous and peculiar striation, which on 

 closer examination appears like a number of raised ribs radiating from the centre to the 

 periphery and divided by intermediary furrows into a great many finer and finer ramifications. 

 The whole has at the first glance a striking resemblance to a ramified complicated system 

 of canals in the walls of the digestive cavity; and a corresponding structure in other star- 

 fishes seems also to have been considered by an earlier naturalist (Tidemann) as a part of 

 the supposed blood-vessel system (stomach veins). Nevertheless on more minute investi- 

 gation, and especially by examining the transverse section of this part, the conviction is 

 soon acquired that here is no real system of canals, but only a peculiar radial corrugation 

 of the roof of the digestive cavity itself, which only appears distinctly on the upper side of 

 the same ; while on the lower side it is completely hidden by the numerous wart-like papillaj 

 projecting in the digestive cavity. 



I have not been able to find any evident central aperture in the upper wall. The 

 whole digestive cavity appears to be quite closed, without any part being discoverable that 

 can properly be called an intestine. There may indeed be remarked on the outside of the 

 dorsal skin of the disc a fine opening or pore (Tab. 1, fig. 4, 7 a) which according to its 

 position might easily be taken for an anal aperture ; but I consider it certain that this is 

 not the case. It is, as will be shewn in the sequel, only the exterior outlet for a strongly 

 developed glandular organ which has its place in the middle between the stomach and the 

 dorsal skin, and which answers to the so-called interradial ciEca in other star-fishes. 



c. The radial caeca. 



These organs, which are peculiar to the proper star-fish and entirely wanting in the 

 Ophiurse, and which must be considered as special sections of the digestive cavity destined 

 for the individual arms, are also very distinctly developed in the Brisinga. Even if they do 

 not, as in other star-fishes, extend right into the points of the arms, they are yet in pro- 



