456 JOURNAL OF SCIENCE. 
found immense numbers of embryos with the valves of the larval 
shell covering the sides of the body, and adherent to the inner 
surfaces of the glass vessels. In some places upwards of twenty- 
five might have been counted to the square inch. Every avail- 
able part of the surface of the vessels was, however, more or less 
affected by these affixed embryos. Some of the jars were then 
taken from the closed circuit, and a continuous current passed 
through them, which it was found did not dislodge the embryos, 
but in two or three days more it was found that most had died 
or been detached, even in the portion of the apparatus not affected 
by a continuous current of fresh sea-water. The gratifying re- 
sult which we had anticipated at the beginning of our experi- 
ment was, however, not realised, except in so far as it determined 
that fixation of the embryos tool place at an early period under 
favourable conditions, or in about twenty-four hours, and that 
they might be reared from artificially fertilised ova. Efforts to 
repeat our first successful experiment failed, owing probably to 
to the high temperature then prevailing. 
The next advance made was when the writer hit upon a phy- 
sical test by means of which the sexes of the spawning adults 
can be instantly determined by the most ignorant person. It 
was found that, if the ova were squeezed from the ovary, and 
dropped into sea-water in a glass dish resting on a dark ground, 
they would break up into a distinctly granular cloud ; while the 
milt would not so readily break up, but would tend to mix slowly 
with the water as a milky substance, the particles of which were 
not perceptible to the naked eye, and, if stirred about in the 
water, would not break up at once, but be drawn out into wisps 
and streaks resembling in miniature cirrus or mares-tale clouds. 
This test was an infallible guide; so much so, that a pocket-lens 
was found to be of no advantage, as we had formerly supposed. 
We also found that if the eggs did not separate at once, when 
dropped into the water, they were not so mature as they should 
be. 
Another important improvement was also introduced by the 
writer for extracting the eggs and milt from the adults for spawn- 
ing purposes. This consisted in applying essentially the same 
method for the extraction of the eggs as is used in spawning 
fish artificially ; thereby avoiding the admixture of foreign mat- 
ters, and fragments of the other tissues of the animal, such as 
occurs when the ovary is cut out and chopped up into fragments 
in water. A very little experience will enable a person to find 
the ovary or spermary on the sides of the body of the animal 
when one valve is removed. Removing the mantle below and 
in front of the heart-chamber, its principal ducts will be exposed, 
and these may be traced backwards on either side of the ventral 
process of the body-mass to below the muscle, where the process 
juts into the suprabranchial chamber with its apex reaching to 
the commencement of the cloaca. When the spawn is abundant, 
the ducts are usually gorged, and look like prominent veins dis- 
tended with a creamy substance. 
