164 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
all the more certain from the characteristic appearance of the ovaries of certain 
lobsters taken in summer in the very midst of the spawning season. There are 
certain infallible signs which prove that the ovarian eggs are due in the current 
season, the most conspicuous of which is the color change. From a light pea-green 
the ovary becomes a dark olive or rather a greenish-black color, which is often 
noticeable at the very beginning of the period of rapid growth, or at least when 
many of the ova are scarcely more than £ mm. in diameter (see fig. 5, «), and not due 
for some weeks. Then with the further growth of the ova the transparent elastic 
wall of the ovary becomes distended and assumes, a beaded appearance. As the 
period of ovulation approaches, the ovarian eggs become free, and, if the wall is cut, 
flow out in a stream. It is thus evident that during the second year the ovary under- 
goes little change with respect to the size of the ova up to the beginning of summer 
or of the second period of rapid growth. Further direct observations upon lobsters 
kept alive for upwards of ten months after the hatching of a brood demonstrate that 
their ovarian eggs attain that size which the theory of biennial spawning demands. 
Accordingly, a very slight change from the condition shown in stage 2 ushers in 
a second period of rapid growth, and this period, beginning usually sometime in June 
or early July, is brought to a close in the course of a few weeks, when the new gen- 
eration of eggs is extruded. 
The rapidity of growth of the ovarian eggs for a period of six weeks, as meas- 
ured from the initial stage bv means of the chronometer provided by the eggs 
attached to the swimmerets, is illustrated by figures 4 and 5. The egg more than 
doubles in volume during the first fortnight, while in seven weeks the initial volume 
has been increased 9.3 times. 
While we speak of “stages” and “periods of growth” as a matter of conven- 
ience, it is hardly, necessary to bo reminded that every change is gradual, and that 
no abrupt transitions are known. 
The theory of biennial spawning is supported: (1) By the statistics of the 
fishery; (2) by the anatomy of the ovary of the adult female taken at different 
seasons; (3) by the ratio of growth of a given generation of ovarian ova for stated 
periods; (4) by observation on animals kept alive for long periods; (5) b} r the evi- 
dence of the rapid growth of ovarian eggs of spawners for any given year during 
the height of the breeding season. 
It is to lie expected that the rule to which the majority conforms has many 
exceptions in individual cases, for variation is the rule of life. It seems quite probable 
that occasionally a lobster may lay eggs in two consecutive -seasons, and that in other 
cases the normal biennial. period may be even prolonged, but I have nothing to offer 
under this head. 
I have shown in an earlier work* that a considerable number of spawners laid 
their eggs out of season, as in the fall and winter months. How can we account for 
these fall and winter eggs? An experiment tried by Mr. Cunningham, f in the 
summer of 1897, on the European lobster, suggests an answer to the question. At 
Falmouth, England, five female lobsters bearing external eggs about ready to hatch 

* Ibid, p. 44. 
f Contributions to the knowledge of the national history of the lobster and crab. Journ. Royal Inst. Cornwall, No. 
xliv, 1897. 
