170 
THE STARFISH FAMILY 
circular plate. It is known as the madreporic plate (mad-re- 
phr'ik: Greek, mater , mother; poros, soft). It serves to 
take water into a series of vessels by means of which the 
animal moves and holds on to rocks and shells at the sea 
bottom. 
Internal Structure. — If the upper portion of the animal 
is removed carefully, the internal structure can be examined. 
Each ray is nearly filled with masses of yellowish green 
substance. This is a gland which forms the digestive fluids 
used in the stomach. The wrinkled mass in the region 
A, liver; B, stomach; C, mouth; D, stone canal through which the 
water enters that is used in the organs of locomotion; E, tube feet; F, re¬ 
productive glands. 
beneath the disk is the stomach. The mouth is just below 
the stomach on the lower or oral side of the body. At the 
angles of the arms and extending into each ray are the 
reproductive glands, which vary in size at different ages and 
seasons. According to the sex of the individual these glands 
produce either eggs or sperms, which are discharged into the 
water. 
LABORATORY STUDY 
Dried specimens of starfish serve well for general study. These may 
be compared with specimens which have been preserved in alcohol or 
formalin. Work out the several parts such as disk, arms, madreporic 
plate, spines, groove of the feet, and position and form of the mouth. If 
skeletons of sea-urchins are available, they are interesting for comparison. 
