238 PHILIP B. HADLEY. 



in length do not molt oftener than twice in a year ; once in the 

 spring or early summer and once in the autumn. Thus the aver- 

 age lobster enters the twentieth stage some time in the autumn of 

 his fourth year and at this molt increases from 162 mm. to 181 

 mm. (7% inches). In the late spring or early summer of the 

 following year the lobster, now approximately four years old, 

 enters the twenty-first stage with a corresponding length of 200 

 mm. (8 inches). 



If the case is not one of a young female bearing external eggs 

 (very rare in lobsters of this length), we may expect another molt 

 the following autumn and consequently find the lobster in the 

 twenty-second stage now with a length of 222 mm. (8^j inches). 

 In all probability the molting periods of the male and female re- 

 main the same until past the nine-inch length. Therefore, the 

 entrance to the twenty-third stage probably takes place just be- 

 fore, or at any rate soon after, the lobster becomes five years old. 

 The corresponding length is 247 mm. (9^5 inches). 



By the time this length is reached many of the female lobsters 

 are sexually mature and are bearing external eggs. Owing to 

 this fact, from this time on the rate of growth of the females must 

 be much diminished. This is due no doubt to the checking of 

 the growing process, a phenomenon which very naturally pre- 

 cedes the spawning period ; also to the length of time (ten to 

 eleven months) the eggs are carried. The male lobsters, on the 

 other hand, maintain their former rate of development so that by 

 the twenty-fourth stage the average male lobster has a length of 

 275 mm. (11 inches) and cannot be much less than six years 

 old. In the case of the females, however, which have borne eggs 

 since the nine-inch stage, the eleven-inch limit cannot be attained 

 in a shorter period than eight years. 



This discrepancy in the rate of growth of the male and female 

 lobsters from this time on, is undoubtedly the explanation of the 

 fact that, in nearly all individuals in which the sex has been ob- 

 served, the " giant ' lobsters have been of the male variety. 

 There are few data on the rate of growth of large lobsters but it 

 is probable that after the ten-inch size has been attained, the lob- 

 ster does not molt oftener than once in a year ; and after the fif- 

 teen-inch stage not oftener than once in two years. Regarding 



