NATURAL HISTORY OF THE BAY SCALLOP 
613 
the gonads has been found consistently. A scallop might have much new growth 
and gonads far from empty or little new growth and gonads nearly emptied. Although 
such cases are extreme, it seems clear that the significant factor is not spawn emission. 
If growth cessation is causally connected with the spawning season (and such a 
hypothesis is deemed worthy of tentative acceptance) it would seem that some 
metabolic activity, indirectly connected with the development of eggs and sperms, 
must be responsible. 
In this connection it is interesting to note that Kisser (1901) working in Rhode 
Island and Belding (1910) working in Massachusetts, arrived at opposite conclusions 
as to the factor producing the annual-growth line. Risser found the spawning season 
to correspond well with the month of June and the growth line to be formed by an 
interruption of growth during that month. His growth curve, although it leaves 
such a possibility, does not show complete growth cessation during June. Neither 
does it definitely show growth cessation during the winter, but it indicates that if 
growth had ceased it was resumed by mid March. His photographs of scallop shells 
show no growth line by May 31 (too late, it would seem, for a winter line) but a 
noticeable resumed growth on shells taken July 1 to 12 and, therefore, indicate that 
the growth line was formed in June, the spawning month. 
Belding (loc. cit.) states that the growth line is due to growth interruption not 
in the spawning season but rather in the winter months. In support of this assertion 
he gives various growth curves showing complete cessation of growth from December 
1 to May 1, with a sharply marked resumption of growth on May 1. Instead of 
cessation of growth during the spawning season (June-July) he found a reduced 
growth rate (also shown in graphs). His excellent photographs of scallop shells 
with and without growth lines, bear no dates and, therefore, furnish no evidence 
pro or con. His graphs, with the sharp rise through May, the reduced inclination 
through June and July, and the increased inclination through August, September, 
and October, plainly indicate winter (and spring) cessation rather than spawning 
season cessation as productive of the growth line. However, it is to be considered 
that the time between growth resumption and spawning is short (about a month) 
and that not the act of spawning but rather metabolism connected with., egg and 
sperm development may be the factor causing growth cessation. The fact that 
growth is shown through a period does not preclude the possibility that there has 
been a cessation at some interval or intervals during that period ; that is, that a second 
growth interruption may have occurred. Moreover Belding’s growth curves consist 
of a series of connected straight monthly lines connecting single points for each month. 
No collection dates nor data as to the numbers measured are given, and there is 
nothing to show that measurements were made at closer intervals as would be neces- 
sary to preclude the possibility of growth cessation going unrecorded. 
To a degree my investigations tend to corroborate the findings of Risser and to 
oppose those of Belding as to the factor affecting the annual-growth line. Further- 
more certain possibilities for error in Beiding’s conclusions are suggested (see pre- 
ceding paragraph). It is, however, altogether reasonable that in northern areas the 
severe cold would stop growth and that the vernal resumption of growth, especially 
with a rapidly growing animal, would leave a well-marked growth line. Even if 
growth ceased for a time during the spawning season, the effect of this might be merged 
with the recently formed winter line. 
Hopkins (1930) quotes Belding as to age and growth of Massachusetts scallops 
and the present writer as to Beaufort scallops. 
