92 
THE PEARL OYSTER 
when the valves are open for breathing and feeding, the 
animal is at rest, and has to exert its strong adductor muscle 
only when on its guard against enemies. The pearl oyster 
breathes and feeds like the English oyster which is so ad- 
mirably described^ with excellent illustrations, by Professor 
Huxley in the October and November numbers of 1883 of 
the English Illustrated Magazine. Both are alike acephalous, 
or headless, and eyeless, except in the larval state, though 
both have mouths and labial palps or lips like flaps with 
which to select food and convey it to the mouth. Both are 
extraordinarily fertile, the pearl oyster spawning, according 
to Dr. Kelaart, almost from its birth, certainly during the 
months of March, April, May and J une, not from July to 
September, the gap from October to March being unknown. 
One pearl oyster contained, under Dr. Kelaart' s micrometer, 
as many as twelve million ova. The larva of both floats 
and has been presiuned to be at the mercy of the currents, 
a presumption to which in my view a certain amount of 
reservation is to be attached. 
Migratory liahits. 
The migratory powers of the pearl oyster as distinguished 
from the sedentary habit of the edible oyster arrest our 
special interest. From the date of its birth the pearl oyster's 
first migratory property is to float on the surface, and be 
carried to and fro by the superficial currents. In some 
measure therefore it probably depends on what are the upper 
currents that prevail during the days that it is afloat, where 
the larva is when it comes to an age to be precipitated as 
spat, though it seemingly has also the means of propelling 
itself in the water by the action of a natatory organ called 
the velum, like the wheel at one end of the roti/cnv, so that 
it can direct its course to any particular object that it may 
wish to adhere to. I say " seemingly," because it was only 
through a hand-glass that I had but once the opportunity 
