NATURAL HISTORY OF THE BAY SCALLOP 601 
Table 3. — Numbers of scallops 2 millimeters or less in length taken in the various “grass” collections 
at Pivers Island from January, 1927, to January, 1928 
[When one collection was made during a period of 3 or 4 days, a central date is given. (See flg. 20.)] 
Date 
Number 
Date 
Number 
Date 
Number 
1927 
1927 
1927 
164 
May 19 
0 
37 
140 
June 3 
1 
Oct. 11 
227 
92 
June 25 
1 
Nov. 9. 
289 
2 
July 8 
1 
Dec. 23 
66 
Mar. 20 
2 
July 23 
1 
0 
Aug. 2 
8 
1928 
0 
Aug. 22 
43 
Jan. 25 
216 
0 
Sept. 6 - 
204 
SPAWNING 
As previously noted, the ovary and testis for each side open through a common 
duct into the kidney of that side, and thence through the urinogenital opening into 
the suprabranchial space, with its exhalant current. Eggs, pink or almost red in mass, 
and sperms, white or cream, supposedly and apparently are discharged separately to 
the exterior so that self-fertilization is the exception. Self-fertilization has been 
obtained experimentally by Risser (1901), Belding, and the writer under artificial 
conditions. Certain observations of Kellogg suggest that frequently a small number 
of eggs may be self-fertilized under natural conditions, for Kellogg (1892) frequently 
found a few developing eggs in the kidneys. It seems more probable that these were 
fertilized either in the kidney or in the common gono-duct by sperms emerging through 
the same passage than by entering sperms from another individual. Relding has 
noted in rare cases a simultaneous discharge of eggs and sperms. 
Belding (1910) induced spawning by transferring scallops from relatively cool 
water to jars of water placed in the sun to warm. Risser (1901) and Drew (1906) 
confined scallops ready to spawn so that these investigators might obtain eggs and 
sperms, but seem not to have attempted to induce spawning. I made many attempts 
to apply Belding’s method, but failed so frequently as to suggest that temperature 
rise is not a very effective stimulus to spawning, which would not be surprising in a 
region where scallop spawning occurs principally during a period when water tempera- 
ture is declining. An alternative explanation is that the extended spawning season 
gives relatively small chance of finding scallops just ready to spawn. 
As previously noted, spawning was obtained as early as August 26. Two scallops 
were placed in separate bowls of water at 25° C. Sea water heated in a flask, closed 
except for a condenser tube, was added to these bowls until the temperature was 
raised in one case first to 28.5° C., and then to 32° C., in the other case, first to 29.5° C. 
and then to 30.5° C. When in a few minutes the water which had stood at 32° C. 
dropped to 30° C., the scallop in that bowl began to spawn, casting out both sperms 
and eggs, many of the latter in small chunks and apparently not fully matured. “Self- 
fertilization ” occurred and in 1 hour and 20 minutes 3-celled (or possibly 2-celled with 
yolk lobe) embryos were numerous. 
From this experiment vast numbers of embryos were obtained. In one day 
most of these were in the gastrula stage, in two days either in the trochopliore stage, 
or with shells developed. Some of the shelled larvae remained alive six days but 
made little growth. 
