May 18, 1900.] 



SCIENCE. 



793 



berger's forthcomiug, detailed and fully illus- 

 trated account. 



Geoege Grant MacCuedy. 

 Yale Univbesity. 



CERTAIN LA WS OF VARIATION* 

 In a former paper fit was shown that the 

 ova of the Echinoid Strongylocentrotus lividus 

 were extraordinarily sensitive to their environ- 

 mental conditions at the time of impregnation. 

 For instance, by keeping the mixed ova and 

 sperm in water at about 26° or 28° C. for an hour, 

 the plutei obtained after eight days' develop- 

 ment were some 5 per cent, smaller than those 

 from ova kept at about 20° at the time of im- 

 pregnation. 



These observations were repeated and con- 

 firmed, in the case of Spheerechinus granularis as 

 well as Strongylocentrotus, and others were made 

 upon the reaction of Strongylocentrotus to en- 

 vironment in the later stages of their develop- 

 ment. Thus after keeping the ova at a normal 

 temperature for an hour at the time of impreg- 

 nation, a portion of them was exposed to an 

 abnormal temperature. After a few hours 

 some of these were re -transferred to water at a 

 normal temperature, and kept there for the re- 

 mainder of development. A few hours later, 

 some more of them were transferred, and so on. 

 By measuring the larvte after six or eight days' 

 growth, the effect produced by various periods 

 of exposure was determined. When the ' nor- 

 mal ' temperature was 20° and the abnormal 

 about 8°, it was found that the larvae were 

 diminished on an average 1.3 per cent, for each 

 hour's exposure between the end of the 1st to 

 the end of the 6th hour after impregnation ; 

 0.3 per cent, for each hour between the 6th and 

 10th hours; and 0.2 per cent, for each hour 

 between the 10th and 21st hours. When the 

 'normal' temperature was about 13° and the 

 ' abnormal ' about 20°, an increase in size was 

 produced, amounting to 1.1 per cent, per hour 

 during the 5th hour after impregnation ; 0.4 

 per cent, during the 14th hour; 0.13 per cent, 

 during the 46th hour, and 0.01 per cent, during 



* Abstract of a paper read before the Royal Society 

 on March 29, 1900, by Dr. H. M. Vernon, Fellow of 

 Magdalen College, Oxford. 



t Phil. Trans., B, 1895, p. 577. 



the 120th hour. That is to say, in each ease 

 the effect of temperature on the growth diminished 

 regularly and rapidly from the time of impregna- 

 tion onwards. 



When the ova were exposed to an abnormal 

 temperature of 26°, an adverse effect of 4 per 

 cent, was per hour produced during the first 

 three hours. For the next four hours the effect 

 was almost nil, and after that a favorable effect 

 on growth ensued. This was about 0.4 per 

 cent, per hour for the 16th hour, and 0.01 per 

 cent, for the 80th hour. This change of reac- 

 tion was accounted for by the fact that the fatal 

 temperatuie, and therefore also the tempera- 

 tures unfavorable to growth, rise during devel- 

 opment. Thus the death temperature is 28.5° 

 for ova, 33.5° for four hours' blastulas, 36.5° for 

 12 hours' blastulae, and 40.3° for six days' 

 plutei. 



The effect of change of salinity on the growth 

 was also found to diminish rapidly with progress 

 of development, hence probably a similar rela- 

 tionship would show itself for other conditions 

 of environment. 



What is true for echinoids is probably true 

 for most other organisms, or is, in fact, a law 

 of general application. Thus in man the rate 

 of growth during the third week of embryonic 

 existence is about 2400 times greater than be- 

 tween the 13th and 19th years of post-natal 

 development. The reaction to environment 

 must also be much greater during the earlier 

 period, thereforej though not in the same pro- 

 portion. Thus, in that the variability dimin- 

 ishes considerably during development — Minot 

 has shown that it becomes halved through the 

 post natal growth of guinea-pigs — retardations 

 or accelerations of growth produced in the 

 young animals must also become partly wiped 

 out by the time the adult stage is reached. 



By splitting up into groups the 20,600 meas- 

 urements which have been made from time to 

 time on Strongylocentrotus larvae, according to 

 the amount of effect which had been produced 

 in their size by varying degrees of favorable 

 and unfavorable environment, and by deter- 

 mining the average variability of the larvae in 

 each group, it was sought to prove the exist- 

 ence of a law of variability. This may be 

 worded as follows : " An organism varies least 



