360 
bulletin of the bureau of fisheries. 
Of extrinsic causes the most important are (a) food of the proper sorts, (6) changes 
in temperature, a powerful factor under ordinary conditions, and (c) changes in light, 
to which the lobster, whether as larva, adolescent, or adult, is very sensitive from infancy 
to old age. 
Every stage period culminates in molting, a result and expression of growth which 
is subject to the causes above enumerated and therefore indeterminate. Consequently 
the rate of growth in lobsters is subject to wide variation. Every individual has its 
own rate, which may vary from that of others or from its own rate at a later period of 
life by ioo per cent, and which may be different at different times of the year and at 
different places, as well as different at corresponding times in different years at the 
same place. Moreover, beyond a certain stage the rate of growth varies in the sexes. 
Variation in the rate of growth is far from uniform in man and the higher animals, but 
it is not subject to such rapid changes and wide fluctuations. 
Notwithstanding the drawbacks and difficulties of the problem, it is possible to 
determine the average rate of growth and age of maturity, provided our statistics are 
ample, which is not the case at present except for one or two points on the coast. 
RATE OF GROWTH AND AGE AT SEXUAL MATURITY. 
In 1895 I made the first systematic attempt to determine how long it takes an 
adult marketable lobster to grow, and remarked: “It is impossible to answer the ques- 
tion with certainty, since complete data for solving the problem have not been gathered. 
We can, however, give a tentative answer which is probably not far from the truth.” 
It was further pointed out that in order to ascertain the average age of a lobster 
io}4 inches long (weight 1J4 pounds) it would be necessary to know, first, the number 
of molts which the animal had passed through, and, secondly, the time interval between 
each molt. We showed that the number of molts could be approximately determined 
by certain means discussed. The time interval could only be ascertained by keeping 
the animals alive for a period of years and carefully recording their growth. Both of 
these factors, as we have already seen, are highly variable quantities. Thus, to give 
further examples, the length of a certain yearling lobster which was raised from the egg 
was only 36 millimeters, while three other lobsters measured from 35 millimeters to 51.8 
millimeters when only 5 months old. Even more striking individual differences have 
been given by Mead (195) and Hadley ( 126 ); two of Professor Mead’s lobsters each 4 >2 
months old (June 1 to October 7) measured about 55 millimeters and 30 millimeters, 
respectively, the smaller being not much larger than one of the big claws of the former. 
Of three lobsters figured by Hadley, each having attained an age of x year and 4 
months on October 23, 1902, the larger had reached a length of about 120 millimeters 
(nearly 5 inches), the smaller but 58 millimeters (about 2 l 4 inches). Lobsters that 
live in harbors where they find abundant food undoubtedly grow much faster than 
those farther from shore and on poor feeding grounds. It could hardly be expected, 
moreover, that lobsters kept under artificial conditions would grow as rapidly as when 
free in the ocean. 
