No. 457.] CANADIAN OYSTER. 43 
as in, or very near, the median transverse plane of the body. 
Here it passes dorsalwards, between the first gill-filaments, ex- 
panding into the stomach with its large lateral liver-sacs. The 
intestine passes backwards towards the right, and then forwards 
towards the left, when it again turns backwards and upwards in 
the left umbo, and finally downwards in the median plane, over 
the posterior adductor muscle ; the greater part of its folds lie in 
the larger, left valve. In front and above the velum is a trans- 
verse adductor muscle, while below the posterior parts of the 
umbos is a larger, transverse, posterior adductor muscle ; retrac- 
tor fibers converge from the velum to points in the umbos. 
Right and left mantle-folds line the inner surfaces of the valves. 
Examination of eel-grass, rock-weed and other marine plants, 
of shells, stones, sand and other objects, revealed no young spat. 
Bundles of brush were tied to submerged rocks, or weighted 
with stones and sunk at various places. These were carefully 
examined at intervals but without result. Window-glass was” 
cut into strips 2 x 6 in. and stood on end in crocks, about 
a dozen in each held apart by wire racks, the crocks being then 
set out below low-water level on oyster beds and made secure by 
zuilding stones around them. Daily examination of the glass 
was made until, on the 16th Aug., I found my first young 
oyster-spat. It measured 1.030 X .876 mm. in length and depth 
and exhibited the characteristic coloration of the pelagic larva. 
In the centre of its dorsal surface could be distinctly recognized 
the shell (prodissoconch) of the oldest free-swimming stage 
(.384 X .369 mm.), securely fixed to the glass by its left valve. 
The anterior adductor appeared to be moved slightly backwards 
and upwards from its original position, and the posterior adduc- 
tor had moved downwards and backwards to a position outside 
the border of the prodissoconch. Behind it opened the rectum. 
In front of the adductors and in a direction parallel with them, 
slanting downwards and backwards, were the axes of two sets of 
gill-filaments, the deeper (left) of sixteen long filaments with 
their free ends pointing forwards or forwards and downwards, 
the upper (right) of about half that number of short filaments 
that ceased below the posterior adductor muscle. No foot 
could be recognized. The new spat shell was very thin and 
