Contributions from the Biological Laboratory of the U. S. Fish Commission, 
Woods Hole, Massachusetts. 
THE REPRODUCTIVE PERIOD IN THE LOBSTER 
By FRANCIS H. HERRICK. 
Whenever it is impracticable to determine the reproductive periods in an animal 
by watching its behavior, the structure of the ovary will usually furnish a clew. This 
is true of the Crustacea, and probably of all other animals. My present aim is not 
only to illustrate this fact, but to settle certain questions concerning the breeding 
habits of the American lobster about which doubt is still expressed. To state the 
question briefly: How often does the adult animal lay eggs? — Every year, once in 
two years, or at longer intervals, for these diverse answers have been given by 
various writers. 
Over ten years ago 1 found that a study of the comparative anatomy of the 
ovaries taken at different seasons seemed to prove the impossibility of annual 
spawning,* and to demonstrate that eggs were not laid of tenor, as a rule, than every 
other year. This was further illustrated in a fuller work published in 1895. f While 
confident that these conclusions were reliable, the main evidence in their support was 
indirect, as I took pains to state at that time. It is now possible to supplement 
these earlier observations by direct experiments upon living animals, and the theory 
of biennial spawning is supported by a variety of testimony. The true answer to 
the question, How often does the mature lobster lay her eggs? is, therefore, Once 
in two years, as a rule. 
We will now consider the evidence upon which this conclusion is based. Apart 
from the question of the frequency of spawning, the following facts are known: (1) 
The majority of the egg -producers for any given year lay at a definite season — namely, 
in summer. The breeding or egg-laying - season at Woods Hole, Massachusetts, 
reaches its height during the latter part of July. (2) Following ovulation comes a 
long period of fosterage, inaccurately called incubation, which lasts from ten to eleven 
months, during which the eggs are carried under the “tail” or abdomen. (3) The 
hatching of this generation of external eggs follows in Mav or June. 
To revert now to the question of the frequency of spawning. Do the berried 
females whose young hatch in May, 1902, lay again in July of that year, or not 
until July, 1903, or in some subsequent year? 
In 1895 I recommended that the direct experiment should be tried of keeping- 
female lobsters alive from the period of the hatching of their last broods until the 
* Notes on the Habits and Larval Stages of the American Lobster, Johns Hopkins University Bulletin, No. 88, May 1891. 
t The American Lobster; A Study of its Habits and Development. U. S. Fish Commission, Washington, 1895. 
161 
F. C. B. 1901—11 
