[11] THE OYSTER AND OYSTER-CULTURE. 693 
Longitudinal cross-section of a seven or eight years old oyster. 
The curved left valve (1K) of the shell is, as usual,” 
somewhat thicker than the right (rf). They are 
bound together by the ligament L, which keeps them 
separated a certain distance from each other so long 
as the adductor muscle (gS and wS) does not by its 
contraction stretch the ligament and close the valves. 
The shell-muscle consists of fine gray (gS) and coarse 
white muscular fibers (wS). In the neighborhood of 
L the ligament, in the left valve, are four small perfora- 
tions made by a sponge (Clione celata) which lives 
housed in the oyster-shells of the sea-flats. Other 
larger holes are often found in the shells of old 
oysters. They are filled with w ater, which has a rank, 
gaseous smell; hence they are eid! “oas-holes.” The 
os thickest part of the shell is near where the shell-muscle 
is attached. The shell consists principally of carbon- 
ate of lime, arranged in firm, glistening layers. Close 
above the shell-muscle lies the heart (H). The mass 
over the heart, which in life is of a bright color, con- 
sists principally of the organs of generation (G). 
These surround the stomach (Ma) and the liver (L), 
which during life is brown in color. In the space 
i above the intestines is seen the sections of the four 
ik; mouth-plates(-Mp). Under the shell-muscle and close 
to the shell are the two mantle-lobes (Mt), whose 
edges are thickened and beset with fringes. They 
contain muscle and nerve fibers. During life the man- 
tle-lobes can be thrust out over the edge of the shell. 
From the edges of the mantle-lobes all the shell material is secreted. Between the 
two mantle-lobes there is a wide space, in which hang the four gills (Kt). Each gill- 
ws! 
Fira. 5. 
spermatozoa; in many others I found spermatozoa, but no ova; “and ‘in seven oysters 
which bore embryos of a blue color upon the beard I found spermatozoa in the genera- 
tive organs. 
Three oysters with embryos of a white color attached to the beard had no sperma- 
tozoain the generative organs. Most mature oysters produce either ova or spermatozoa, 
and not both at the same time. Of 309 oysters which were dredged on the 25th of May 
from four different beds along the east side of the island of Sylt, and which were ex- 
amined from the 26th of May to the ist of June, the sex of 18 per cent. could not be 
determined ; of the remaining 82 per cent., one-half were males and one-half females 
In none of them were the generative products completely matured. From these results 
I conclude that the ova and spermatozoa do not arise in the generative organs of the 
oyster contemporaneously, but that one follows the other. The spermatozoa can arise 
ery soon after the expulsion of the ova, and probably one-half of the oysters of a ter- 
ae during any spawning period produce eggs only, the other half spermatozoa only, 
\\/ a. Amass of spermatozoa, still clustered together just as 
they arise in the generative organs, enlarged 275 tines. 
b. Asingle spermatozoan, enlarged 1,000 times. By the 
motion of the tail the body is driven forward. 
/ The ripe spermatozoa pass from the generative organs 
into the water, with which they pass into the brood- 
chamber of the female oyster, where they impregnate the 
h freshly-laid eggs by penetrating the yolk and uniting 
\ with it. 
lia. 6. 
