50 THE PEINCIPLES OF HEREDITY 



neighbourhood of Freiburg. The colour of one variety, A, is 

 light yellow-ochre, five green spots being present on either 

 side of the shell ; the other variety, B, appears dark green, 

 owing to the yellow-ochre ground-colour being reduced in 

 extent by the presence of six large green patches. ... In 

 1887 some individuals of the dark green variety, B, appeared 

 for the first time in an aquarium containing the typical yellow- 

 ochre-coloured variety, A ; and since 1 have observed a similar 

 occurrence in other broods of A. . . In the winter of 1890-91 

 a colony of B appeared in which a few typical individuals of 

 the variety A were found together with typical specimens of 

 B which had been bred in this aquarium for years." J 



85. Still more recently Dr. E. Warren has published careful 

 measurements made on Daphnia Magna. "From twenty- 

 three Daphnia (themselves originated by parthenogesis) 

 broods were produced consisting of three to six individuals. 

 The parents were measured and the offspring allowed to grow 

 up. On measuring the offspring it was obvious that the 

 children of the same brood exhibited very considerable 

 variability. . . . Among my notes are recorded the measure- 

 ments of twenty-six grandchildren, the offspring of seven 

 grandparents. With these the co-efficients of correlation and 

 regression were calculated. On account of the altogether 

 insufficient number of individuals, the results were bound to 

 be very uncertain, but they appear to favour the view that 

 inheritance in parthenogenetic generation resembles that from 

 mid-grandparents to grandchildren." 2 



86. The belief that variations are due solely, or almost 

 solely, to bi-parental reproduction was, therefore, a pure guess, 

 which subsequent observation has proved entirely erroneous. 

 Since the offspring of asexual reproduction exhibit variations 

 in abundance, we have every reason to suppose that some at 

 least of the variations that occur among races that reproduce 

 sexually are not due to the intermixture of dissimilar germ- 

 plasms. On the other hand bi-parental reproduction is 

 undoubtedly a cause of variations. Our endeavour, therefore, 

 must now be to dissociate the variations due to bi-parental 

 reproduction from those due to other cause or causes. The 

 task will not be very difficult, but it will be somewhat lengthy 

 and roundabout. We shall have to consider first the mode in 

 which the offspring develop. In the end we shall find that 

 sexual reproduction, though a cause of variations, is not a 

 cause of " spontaneous " variations. The variations due to it 



1 The Germ-plasm, pp. 344-6. 



2 Proceedings of the Royal Society, 1889, vol. Ixii., p. 154. 



