240 PHILIP B. HADLEY. 



five per cent, and is often inappreciable. The shells of these 

 huge lobsters present every appearance of great age and give 

 testimony to a life of inactivity. Usjng as a basis the observa- 

 tions which led to the foregoing conclusions, the writer has com- 

 piled a table showing the estimated rate of development of lob- 

 sters from the time of hatching to the attainment of the greatest 

 known size. While the data on the first twenty stages have 

 their ground in actual observation, the records of the later stages 

 have been deduced from less positive evidence, and are, to a great 

 extent, speculative. The great variation in the size of lobsters, 

 even of the same age and stage, render it well-nigh impossible 

 to tell off-hand the age of any adult lobster. On the other 

 hand, the size of large numbers of individual lobsters of a certain 

 age must remain not far from a general average, on a basis of 

 which, the approximate age of large numbers of individuals can 

 be determined with a fair degree of certainty. It is this average, 

 together with the correlated age, that the writer has attempted to 

 formulate in the preceding table : 



INFLUENCES ON THE RATE OF GROWTH. 



Among the influences which modify the rate of growth of 

 young lobsters under natural or artificial conditions, are to be 

 mentioned especially the following : temperature, food supply, 

 light, parasites, injuries and individual physiological peculiarities. 

 It is probable that the water temperature and physiological con- 

 dition are the most influential for young lobsters in the ocean. 

 The others enter largely into consideration in the problems of 

 artificial propagation. The frequency of the molting periods 

 and, secondarily, the amount of increase in length at each molt, 

 is directly dependent upon and determined by the prevailing tem- 

 perature of the water ; a difference of twelve degrees may cause 

 the period of growth to the fourth stage to be over twice as long 

 as normally. Thus we find great variations in the rates of growth 

 of lobsters at different points on the Atlantic coast. For this 

 reason it is very probable that the lobsters in the warm waters of 

 Narrangansett Bay may attain marketable size (lOj/z inches in 

 Massachusetts) much sooner than do the Massachusetts or Maine 

 lobsters. 



