REARING OYSTERS. A57 
To remove the generative products without cutting or lacerat- 
ing the reproductive organs, one should be provided witha 
medicine-dropper or short pipette with a curved tip and a com- 
pressible rubber bulb at top. With the curved point of the 
pipette, the ducts of the reproductive organ are gently and 
firmly stroked in the direction of the external opening from 
before backwards. This, if properly done, will force out the eggs 
or the milt ina stream from the genital opening of the side ; 
when the pipette may be applied to suck up the extruded spawn 
and drop it into water without the admixture of any deleterious 
matters whatever. If the soft parts of the oyster have been left 
attached to the one valve, which I have found to be most con- 
venient in practice, the other side of the animal. may be 
treated in the same way, as the reproductive organ has an 
opening on either side of the body. Todo this the head end of 
the animal, next the hinge, is simply thrown back over the 
adductor, the mantel cut open, and the spawn pressed out of the 
ducts of the under side as before. 
By the foregoing method, which is much neater and more 
cleanly than any other, the best spawn is obtained ; and it is 
often possible to impregnate fully ninety per cent of the eggs 
taken. When eggs so treated are placed under the microscope 
comparatively few injured ones will be observed; at any rate 
the result will be vastly more satisfactory than if the animal is 
crushed or chopped up in order togetthe spawn. Many billions 
of eggs might be fertilised in a day by this plan. 
Asa result of the experience with the fixation of the embryos 
resulting from the artificially fertilised eggs, as described at the 
outset, it was determined to investigate the mode of fixation to 
learn if there wasany uniformity about it. I now believe that 
the fixation of the fry is accomplished by the border ot the larval 
mantle, the existence of byssal organs being doubtful. The 
oldest larval shells of artificially reared embryos have the hinges 
of the valves truncated and without beaks or umbos ; while the 
fry on the eve of conversion into spat has a distinct beak to each 
of its valves, which projects anteriorly beyond the hinge-line. 
The valves, at this time are very ventricose, quite symmetri- 
cal, and similar to [Pisidium in form, or in the most marked 
contrast, in respect of shape, with the irregularity of the older 
spat and adult. 
When a large number of very young natural spat is exa- 
mined on their attachments, it will be found that in every case 
the apex of the umbo of both the valves of the larval shell are 
turned towards the left if the hinge-end is directed towards the 
north. It is therefore clear, that when the young attach them- 
selves, they do so constantly by one and invariably the same 
side. Upon examining spat which has just begun to form a 
shelly attachment, we find this to begin at the border of the lar- 
val shell, and to grow outwards, the hinge being continued for a 
time laterally or on a line with that of the larval shell. We may 
also note that the distal free border of the lower valve is the only 
