45 



Although growth takes place by a series of saltations it is 

 evident that it is similar to that of other groups of which we have 

 knowledge. 1. There is a steady diminution of the rate of growth 

 from the beginning of development. 2. Growth is not uniform ; it 

 is subject to external and internal conditions. It is well known 

 from experiment that changes in temperature are of great import- 

 ance in varying development and growth, and the effects have 

 to some extent been illustrated in the above analyses. In the 

 case of a species spread from the Mediterranean to the north of 

 Norway the life-history both in respect to development and 

 growth is liable to a gradual change from the tropical to the more 

 Arctic limit of the distribution. In one or two cases I have attempted 

 to depict the ideal growth apart from external circumstances. 

 But it is clear that the environment is always bringing about 

 variation. The ideal, in other words, may not ever be reached, 

 circumstances are always at work to produce change. For the 

 North Atlantic region generally we can predicate a summer of 

 rapid growth and a winter of slower growth, and we have evidence 

 to prove that in many cases the result is not always ideal or even 

 average, that there is an actual slowing in growth which leads 

 to the reflexion that one of two things must happen, either the 

 size is stunted or life is prolonged. 



In concluding this section it is a pleasure to record, in addition 

 to that already acknowledged, the help I have received from Dr. 

 Caiman, of the British Museum of Natural History, and from 

 Mr. Storrow who devoted a day from duty to measure many of 

 the series utilised in the foregoing presentation. But above all, 

 I might be allowed to say how much we all owe to George Brook, 

 and especially to IVIr. Waddington, for the series of preparations 

 they have made showing the history of many examples of 

 Crustacea for periods extending as will be noted, often for several 

 years. Miss 0. M. Jorgensen, M.Sc, kindly made the drawings 

 (figs. 2-5) of ths larvae of various Crustaceans for this paper. 



