24 



side of the isolated disc, where the arms have been attached (fig. 1 b). From these radial 

 vessels there issue on each side, at short intervals, lateral canals, which supply the paired 

 water-feet and their ampollae with water. 



b. The water-feet and their ampollae. 



The water-feet or ambulacral tentacles, which, as in other star-fishes, represent the 

 most important locomotive organs of the animal, are very strongly developed, and are in 

 structure and arrangement quite similar to those of other star-fishes. They issue in a similar 

 manner from the bottom of the deep ventral furrows which run along the ventral side of 

 the arms and the disc ; and they are here arranged in a double row. At the base of each 

 of them there is on the inside a large membranous bladder or ampolla protruding freely 

 through the so-called ambulacral pores into the interior cavity of the arms, and forming 

 along the upper side of the ambulacral skeleton a double row (see Tab. Ill, fig. 3 c, fig. 4 

 and 17). These ampollae represent contractile reservoirs of water, by the help of which the 

 water-feet can at any time be made to swell or to contract, Similar ampolla? are also ob- 

 served projecting from the ambulacral pores (fig. 1 c) which correspond with the water-feet 

 of the disc. When fully extended, the water-feet in the Brisinga are 2—3 times longer than 

 the arm is broad, and they are curved and twisted in various manners (see Tab. I, fig. 12 — 14). 

 Even in spirit-specimens they will always be found extended far beyond the ventral furrows, 

 whence it seems evident that the water-feet in the Brisinga are not so highly contractile as 

 those of other star-fishes. In form they are (see fig. 22) cylindro-conical or broadest at the 

 base, tapering regularly towards the extremity, where they have a muscular circular suction 

 disc. In the interior, these water-feet exhibit as usual a wide cavity filled with water: their 

 exterior skin is interwoven with numerous close muscular fibres longitudinal as well as cir- 

 cular; but there is no trace of calcareous particles in the terminal disc, nor in any other 

 part of the skin. The before mentioned double rows of water-feet, which extend along the 

 whole ventral side of the arms, are also continued (see Tab. I, fig. 2) immediately on to the 

 underside of the disc itself; so that there are for each arm 4 water-feet which specially be- 

 long to the disc. In a 10-armed specimen therefore the number of the water-feet belonging 

 to the disc will be 40. 



c The madreporic body and the stone-canal. 



The Madreporic body is in the Brisinga, as in the other star-fishes, situated on the 

 dorsal side of the disc in the interval between 2 arms at their issue. It is however here. 

 by reason of the small breadth of the skeleton of the disc, moved out quite towards the 

 edge, where it covers the tubercular projecting upper end of one of the wedge -plates 

 (see Tab. 1, fig. 3, 4, 6 Tab. II, fig. 1, 2, 8, 11, 12 a). It is in full grown specimens rather 



