DEVELOPMENT OF STAR-FISHES. 195 
ing through the morula and gastrula stages, the cephalula 
or larval stage is reached, the mouth, digestive sac and its 
posterior opening being formed, a cephalic end being dis. 
tinguished from a posterior end. The larva is now bilater- 
ally symmetrical. At this time two lobes arise from each 
side of the mouth. These separate from their attachment 
and form two distinct hollow cavities,and by the time the 
larva attains the Brachiolaria stage the development of the 
Fig. 189. —Brachiolaria 
of Asterias vulgaris, en- 
larged, with the star-fish 
Fig. 138. —Bipinnayia with the star- (7) developing at the 
fish budding en, it. €6,a, 9, 9% short end. ‘, seen 
protuberances of the body comparable a ty e*, odd termi- 
with the “arms” of the Brachiolaria ia ora SPE: DEAGUIo 
figured in the adjoining engraving. ar arm; 7. pane ae 
6, mouth; 0, vent of the larva; A, germ water-tabe (ww’) leac ing 
of the star-fish; A, ciliated ‘digestive into oad brachiolar 
tract; ¢, ambulacral rosette a of pee Be a eee 
Hie eae, After Miiller, from arm flier A Aga 
s1Z. 
body of the star-fish begins, for these two cavities subse- 
quently develop into two water-tubes. On one of these cav- 
ities the back of the star-fish is afterward developed, while 
on the other the under side with the feet or tentacles arise. 
The fully-grown larva is called a brachiolaria, as it was 
originally described with this name under the impression 
that it was an adult animal, as was the case with the plu- 
