146 INVERTEBRATE ZOOLOGY 
to the outside through minute pores in the aboral walls of the 
interrays. Two glands will be found in each ray extending 
from the base of the ray toward its tip. The actual size of 
these organs depends entirely upon the sexual condition of the 
animal. In young or immature animals they may be no more 
than half an inch long or less, while in reproducing animals 
they may extend almost to the tip of the ray. The testis of the 
male and the ovary of the female animal do not differ from each 
other in general appearance. In the mature female, however, 
the ovaries have a light-yellow color, while in the mature male 
the testes are white and are less voluminous than the ovaries. 
Exercise 7. Make a semidiagrammatic drawing of the animal 
showing the details of the digestive and reproductive 
systems; label all. 
Remove the stomach and the reproductive organs from the 
body, taking care not to injure the sinuous stone canal which is 
at one side of the former. 
The ambulacral system. This is the most characteristic system 
of organs in the Echinodermata. In the starfish it consists of 
the following organs: a circular canal, called the _ring canal, 
surrounding the mouth; connected with this canal are nine 
minute lobated sacs called the racemose or Tiedemann’s vesicles, 
two being located in each interray except the one in which is 
the stone canal, where but one is present; five radial canals, 
which pass from the ring canal along the median line of the 
ambulacral grooves to the tips of the arms; the ambulacral feet, 
which are connected with the radial canals by short branch canals, 
and also project through the ambulacral pores into the body- 
cavity, where they expand to form small sacs called ampulle; a 
sinuous canal, called the stone canal, which connects the ring 
canal with the madreporic plate; the madreporic plate, a porous 
plate by means of which the entire system is placed in commu- 
nication with the outside sea water. 
