212 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
VIII. What are the habits of the “ fry ” or free-swimming young f The young of 
many marine animals , while far more abundant than the adults , are much more delicate 
and easier of extermination. 
The ripe eggs of the star fish are minute spherical objects, measuring about one- 
tenth the diameter of the head of a small pin. They are discharged from the female 
through minute pores near the base of each arm, into the water, where they may 
become fertilized by the spermatozoa discharged from the male in a similar manner. 
Each egg, soon after it is fertilized, begins to undergo a long series of changes in 
form. During the first stages of development there is little or no increase in size, and 
the egg rests, like a minute grain of sand, upon the bottom. In the course of a few 
hours, however, the internal changes which have been taking place express them- 
selves. Vibratile cilia appear in certain areas on the surface of the egg, which now 
begins to rotate, and soon rises from the bottom as a free-swimming larva. Soon after 
this the mouth and stomach are developed, and the creature takes in food and grows. 
The growth is rapid, and during the next three weeks, more or less, the larva increases 
its diameter about 50 times. Meanwhile various internal organs and several long- 
arms, and other external features, are developed. The older fry are called brachiolaria, 
from the fact that they have so many long arms. One of these brachiolaria of the 
largest size is represented in fig. 3, much magnified. The natural size is shown in 
fig. 4, where two specimens are figured, one on either side of the bit of eelgrass. The 
animal swims by means of the motile cilia, which are arranged in bands, represented 
by the heavy lines in the figure. They form a complicated pattern over the surface of 
the body, and extend out upon the arms. Tbe body is quite transparent, and the tips 
of the arms, which are shaded in the figure, are light red. The larva represented in 
tig. 3 is old, and would probably have set within 12 hours. Already the rudiment of 
the resulting star-fish, the disk-shaped body at the bottom of the figure, can be seeu 
within the brachiolarian. The five crenate lobes on the margin of the disk are the 
beginning of the five arms. The disk itself at this time is already somewhat opaqne. 
When the larva is about to “set,” it attaches itself to some object, like a spear of 
eelgrass, by the suckers, shown at the top of the figure, and then a rapid transforma- 
tion occurs. The whole superstructure above the disk collapses and becomes absorbed 
like the tail of a tadpole. In a few hours the brachiolarian has disappeared, and a 
star- fish proper has taken its place. 
Although the free-swimming larvm have a considerable power of locomotion, and 
can swim from one side of a dish to the other in a few minutes, they can not, of course, 
make headway against the tidal currents, and are carried hither and thither with 
their ebb and flow. Other extensive movements of larvae are executed in response to 
such changing conditions as those of light and temperature; at times myriads of 
them are swimming at the surface, and in 12 hours not one specimen can be found. 
The brachiolarian, like more lowly organized forms of living creatures, although it 
has no eyes, is exceedingly sensitive to light, sometimes being attracted to it, and 
again being repelled by it. According to my experience, they were found at the 
surface in greatest abundance on cloudy or misty days and nights, and were much 
more rare, or absent altogether, on bright, clear days and moonlight nights. On June 
27, for instance, I skimmed the surface with the tow net from 9 until 11 o’clock, and 
not a single larval star was found, although there were millions of the larva} of the 
annelid worm Syllis , and other organisms. The night was clear, with a bright moon, 
and the tide was rising. The next morning, June 28, was cloudy with some rain, and 
