462 BOUNDARIES OF THE SEA 



beliexe that the figures given in the diagram have to be more than 

 doubled — and hardly that. If now, to be certain, the figures are 

 doubled, the conclusion will roughly be about the same as without 

 doing so, namely that 80 per cent of all larval species examined so 

 far will spend less than 6X2, i.e., 12, weeks in the plankton, which 

 is too short a stay to make them long-distance larvae. A few 

 figures will support this view. A surface current of average velocity 

 will take some 22 to 23 weeks to pass from Cape Hatteras to the 

 Azores, some 19 to 20 weeks to pass from Somaliland to the west 

 coast of India, and some 19 to 20 weeks to pass from the coast of 

 Costa Rica to Clipperton Island, that is, much longer lengths of 

 time than are available to 80 per cent of all larval species, even if 

 the figures in the diagram are doubled. However, if we consider 

 that twice the time given in Fig. 1 is possible under certain 

 circumstances, then a 10- to 12-week larval life may very well give 

 the common larval types a chance to cross, for instance, from East 

 Africa to the Seychelles, from the Seychelles to the Chagos 

 Islands, from Ceylon to the Maldives or, in many cases, from one 

 island group inside Oceania to its neighbor group. But this is not 

 what is understood by transoceanic long-distance transport. 



All this smells very much of statistics, and since we are much 

 more interested in the living larvae in the plankton than in 

 diagrams, we had better return to the individual larval groups to 

 see what they actually stand for. The values in Fig. 1 are fairly 

 close to average ones, and the speed of the surface currents, with 

 which we have tried to compare our figures for larval life, are also 

 based on average velocities. What we should actually like to know 

 is the maximum length of pelagic life which any larva will be able 

 to spend in the plankton finally leading to a successful meta- 

 morphosis, and the maximum velocity of the ocean-crossing 

 surface currents in a year especially favorable for larval transport. 

 In other words, we should like to know how long a distance the 

 larvae may be transported during a season in which a maximum 

 length of pelagic life and a maximum current velocity occur at the 

 same time. We must realize that even if such a favorable condition 

 of maximal length of larval life and maximal current velocity 

 might occur, for instance, only once in some hundred years, this 



