METAMORPHOSIS OF STAR FISH. 
43 
The young or larva has now both sides of the body alike. 
At this time two lobes arise from each side of the mouth. 
These separate from their attachment and form two dis- 
tinct hollow cavities, and by the time the larva attains what 
is called the Brachiolaria stage, the development of the 
body of the star-fish begins, for these two cavities subse- 
quently develop into two water-tubes. On one of these 
cavities the back of the star-fish is afterward developed, 
while on the other the under side with the feet or tentacles 
Fig. 43. — Asterias vulgaris, natural size. 
arise. The fully-grown larva is called a brachiolaria, as it 
was originally described with this name under the impres- 
sion that it was an adult animal. Fig. 45 shows the young 
star-fish growing in the posterior end of the larva or young, 
whose body it is now beginning to absorb; finally, the larva 
body disappears. At this time the star-fish is still minute, 
conical disk-shaped, with a crenulated edge. In this con- 
dition it remains probably two or three years before the 
arms lengthen and the adult form is assumed, 
