70 S. HIROTA. 



similar in the older. The subcircular grayish area in this figure represents 

 the outer or perivisceral surface of a remnant of the lower part of the stomach, 

 which is tied into ambulacral plates by the stomach retractor muscules. 

 The oesophagus has a circular border finely folded and it is almost directly 

 communicated interiorly with the stomach having numerous inner folds as 

 well as short diverticula which are more or less projected outwards amidst 

 the retractor muscles. The latter are ten in number, one in each side of 

 every vertebral ridge, and in each band one part is attached to the base of 

 the first ambulacral plate and another part runs for a short distance along 

 the side of the vertebral ridge to which it attaches. Above all, it is the most 

 interesting tact that the muscular bands which belong to the principal arm 

 are not distinguisned from, but are equally developed as all others so that 

 the radial symmetry is not disturbed. 



Fig. 6 represents the proximal portions of the vertebral ridges and a 

 part of the water-vascular system. This figure is also taken from the 

 younger * comet. '* There are the circum-oral water tube with a tendinous 

 wall, running over the adambulacral ossicles. It gives rise to paired stone 

 canals enclosed within the pericardial sac or * Perihiimalcanal des Herzge- 

 flecht ' of Ludwig,^^^ on both sides of the innermost ambulacral plate of the 

 principal arm. Each of these canals, characterized by a lamellar structure, 

 is led into the primitive madreporic plate of the corresponding side, whose 

 inner surface with the end of the stone canal is shown in Fig. 12. Tiedemann's 

 bodies or the racemose vesicles are attached, in a pair, between two adjacent 

 dasal ambulacral plates in every interbrachial angle. The Polian vesicles are 

 five in number and every one makes a deep hollow just below the paired 

 racemore vesicles in every interbrachial angle. They are entirely concealed 

 out of the vertical view but the positions of two of them are shown in Fig. 7. 

 The five radial tubes which run respectively towards the tips of the five arms 

 give rise, on their ways, to pairs of the ampullae in the perivisceral cavity 

 and to pairs of the feet in the ambulacral furrows in the usual manner. The 



* lu the older ' comet ' the vertebral ridges of two arms represented by a and b in Fig. 3 

 touch each other at their proximal ends, and in consequence of it some disturbances are pro- 

 duced in the vicinity. 



