120 
might drift off and form another mass a short distance from the 
first. Facts which seem to bear this out are, that young are 
very rarely found in these masses; all the component individuals 
are in practically the same stage of existence, and of the same 
proportionate size, so far as can be judged; hence, aå percentage 
of juvenile mortality of approximately 100 ?/0o may be adduced from 
the known facts as well as theoretically; again, the dredge will 
sometimes bring up a mass of crinoid remains from a dead bottom, 
upon which there is no other sign of crinoid life, past or present; 
this suggests that all the crinoid. life has been extinguished at 
about the same time, as the various remnants are in approxi- 
mately the same state of wear, and there is no reason to suppose 
that anything but old age was the cause. Much of interest bearing 
on this point could be learned by a frequent examination, at 
regular intervals, of the well known ,,Pentacrinus" ground near 
Havana, Cuba, though a similar examination of some mass of 
" comatulids (for instance the one off the town of Jolo [Sulu]) im 
the East Indian region would probably be more conclusive and 
much easier to undertake. 
The constant drifting away of the young free swimming coma- 
tulids, and their settling down presumably all in approximately the 
same place at some distanceito leeward (in reference to the current) 
of the parent mass would give rise to a new colony of the species 
all the individuals of which would be of the same age, or nearly 
so, the difference between the oldest and the youngest being only 
as great as the maximum duration of the breeding period of the 
parent mass. We do mot know how long this breeding period is; 
Antedon bifida and A. mediterranea have been found with penta- 
crinoids through practically the whole year, though that is, of 
course, n0 argument that the breeding season is of more than two 
or three month's duration in any one locality. At the end of the 
breeding season there would be no more additions to the newly 
formed colony; the individuals already there would increase in size, 
and develop to the adult form. At the next breeding season a 
