THE ROCK STAR-FISH. 41 
6. With the forceps carefully remove the inter-radial czeca. 
Observe the vascular system lying on the interior of 
the perisoma. From the centre radiate five vessels, 
which pass between the calcareous inter-radial septa. 
Each of these, when it gets beyond the inner edge of 
the septum, divides into three, the centre of which 
passes along the middle of the ray. All three send 
out branches on either side, which are connected with 
the membranous tubuli seen when examining the 
exterior of the animal. 
7. Pass a needle through the anus from the outside. Ob- 
serve its position from the inside with reference to 
the madreporic tubercle, and the centre of the dorsal 
vascular system. 
8. Examine the reproductive organs. They consist of 
ten bunches of tubuli, arranged in five pairs at each 
of the inter-radial angles, just outside the inter- 
radial septa. The tubuli of each bunch empty 
themselves into a single efferent duct, which opens 
exteriorly through one of the reticulations of the 
dermal skeleton, which opening, however, is not 
enlarged or modified in any way. Cut off a portion 
of one of the tubuli and examine with the micro- 
scope. The gnimal is dicecious, and the organs 
may contain ova, which can be recognised by the 
central pellucid germinal vesicle, if it is a female; or 
if it is a male, they may contain spermatozoa, or only 
minute oil globules. The spermatozoa have a round 
head and a long filiform tail. 
9. Take the ventral, or oral portion. With a brush lay 
out each of the ten ramified radial czeca in its proper 
position. Their function is unknown. They open 
into a shallow pentagonal sac—the pyloric sac—which 
