OU l'i H. M. \Yrni.n. 



originally obtained, <>: taken colirrtively, agin; in .showing that the 

 effect of temperature- on the growth of an organism diminishr- 

 rapidly from the time of impregnation onwards. It is to l>e noticed 

 that the effect produced was, as far as could be ascertained, a perma- 

 nent one. At least it persisted to the full larval growth of the 

 organisms, for the larvae were found to practically cease growing after 

 six to eight days' development. How much would have persisted 

 through the metamorphosis to the adult Echinoid stage is, of course, 

 another matter. 



It seems highly probable that what is tnie for temperature is true 

 for other environmental conditions, and that future research will 

 justify one in assuming the existence of a definite Law of Variation. 

 This might be worded as follows: " Tlte permanent effect of environment 

 on tlie growth of a </r/;"l<,j>iiiff organism diminishes regularly and rapidly 

 from the time of im/nrfpiation onwar<l*." 



It is necessary for me now to make one serious criticism of all these 

 observations, one which I regret to say did not occur to me till after 

 they had l>een completed, and when it was too late for me to put it to 

 u proper experimental test. This criticism depends on the obvious 

 fact that all organisms must be confined within comparatively narrow 

 limits in their powers of growth, so that, for instance, supposing a 

 Strongylocentrotvs pluteus under average conditions attains a size of 

 100, then probably under no conditions whatsoever could it be made 

 to attain a larger size than 120 to 125, or a smaller one than 80 to 

 75. Thus in the most extreme variation noticed in any of the 

 numerous observations made on these larvae, the range ran from 19 '2 

 per cent, above the normal to 18 - per cent, below it. Now supposing 

 that during the first hours of development an embryo is placed under 

 especially favourable conditions, then it may happen that thereby it is 

 stimulated to undergo all, or nearly all, the increased growth of which 

 it is capable. In subsequent hours, therefore, little if any more favour- 

 able effect may be produced, simply because the organisms from their 

 very nature are tumble to show it. 



If this principle be examined in relation to the present experiments, 

 I think it can be shown, however, that though no doubt the relation 

 1>etween the reaction of the organism during the earlier hours to that 

 in the later hours has thereby been exaggerated, yet that there still 

 remains plenty of evidence behind to prove that the diminishing re- 

 action to environment exists in addition. 



Let us first consider the three series of experiments in which the 

 developing ova were kept at 26 or 25. Here a diminution of size 

 amounting to from 7 '36 to 20'76 per cent, is produced by the first few 

 hours' exposure to high temperature, so that after this, when the 

 environment begins to exert a favourable influence, we know that it 

 has at least this range of growth capacity at its disposal, plus what- 





