868 



SCIENCE. 



[N. S. Vol. XII. No. 310. 



Passing now to the biological results, we 

 consider first the work done in England, 

 for it was there, in the home of Galton and 

 Pearson that the new methods found their 

 first application. Of the papers of the new 

 era the first is that of Weldon, 1890, en- 

 titled ' The Vai-iations occurring in Certain 

 Decapod Crustacese. I. Crangon Vulgaris.' 

 Proceedings of the Eoyal Society of London, 

 Vol. XLVII, pp. 445-453. This study was 

 undertaken to test Galton's prediction * 

 that selection would not alter the dis- 

 tribution of frequencies in any race. Wel- 

 don measured four dimensions in several 

 hundred individuals, calculated the means 

 and probable errors, compared the observed 

 and theoretical frequencies and concluded 

 that Galton's prediction is fully justified. 

 He showed, in addition, that the variation 

 in size of the organs measured occurs with 

 a frequency indicated by the law of error 

 and that the ' probable error ' of the same 

 organ is different in different races of the 

 same species. 



Next Weldon obtained measurements of 

 the variation of the shrimp Palcemonetes 

 varians in Plymouth, which have lately been 

 made the basis of comparison with our 

 American shrimps by Duncker and by John- 

 son and Hall. These comparisons have es- 

 tablished that the otherwise very similar 

 English and American shrimps have modal 

 numbers of rostral spines which are re- 

 spectively 4 and 8. In 1892 Weldon studied 

 correlative variation in the prawn Crangon 

 vulgaris and drew the conclusion that a wide 

 knowledge of the specific constants would 

 give an altogether new kind of knowledge 

 of the physiologic connection between the 

 various organs of animals. 



In 1893 Weldon published a, fourth 

 paper, on correlated variations in Carcinus 

 manas, in which he dealt with ratios of 

 various dimensions of the body to the cara- 

 pace length. It was in these studies that 



* Natural Inheritance, pp. 119-124. 



Weldon came across a distribution of fre- 

 quencies which did not conform with the 

 theoretical distribution, and which Pearson 

 subsequently resolved into two symmetrical 

 curves. Weldon found the coeflScient cor- 

 relations between similar organs in different 

 races to be closely alike. 



While Weldon was making these studies, 

 Bateson and Brindley published (1892) 

 their quantitative studies on the length of 

 the forceps of male earwigs, on the length 

 of the cephalic horns of a rhinoceros beetle 

 and on the length of the mandibles and the 

 elytra of a stag beetle. In the first two cases 

 there was a marked discontinuity in the 

 variations. Thus the forceps had modes at 

 3.5 millimeters and 7 millimeters, and the 

 horns had modes at 4 and 9.5 millimeters. 

 In 1895 Bateson gave statistics of the mar- 

 velous variation in color of a chrysomelid 

 beetle, but the data hardly admitted of 

 exact quantitative analysis. 



In 1895, Weldon presented to the Royal 

 Society his first report of the committee for 

 conducting statistical inquiries into the 

 measurable characteristics of plants and an- 

 imals. In this report he gives the results 

 of studies on selective destruction of the 

 rock crab. The climax of the studies of 

 Weldon and his pupil, Thompson, on the 

 rock crab is his presidential address before 

 the British Association (1898) in which 

 he showed that the proportional size of 

 the frontal margin of the crab's carapace 

 had at Plymouth, during the preceding five 

 years, diminished five per cent. Conse- 

 quently he has been able by means of 

 the quantitative method to measure a real 

 evolutionary change. Moreover, he has 

 been able to put his finger on the cause of 

 this change, for he showed that the silting 

 up of the harbor of Plymouth, and the 

 greater quantity of mud in the harbor, tends 

 to kill off the crabs with broad gill-openings 

 and to let survive only those with narrow 

 gill-openings and a narrow gill (or frontal) 



