MERISTIC PHENOMENA 45 



ductive organs of the female are deformed and sterile, being 

 known as a free-martin. The same thing occasionally happens 

 in sheep, suggesting that in sheep also twins may be formed by 

 the division of one ovum; for it is impossible to suppose that 

 mere development in juxtaposition can produce a change of this 

 character. I mention the free-martin because it raises a question 

 of absorbing interest. It is conceivable that we should interpret 

 it by reference to the phenomenon of gynandromorphism, seen 

 occasionally in insects, and also in birds as a great rarity. In 

 the gynandromorph one side of the body is male, the other female. 

 A bullfinch for instance has been described with a sharp line of 

 division down the breast between the red feathers of the cock 

 on one side and the brown feathers of the hen on the other. 

 (Poll,H., SB. Ges. Nat. Fr., Berlin, 1909, p. 338.) In such cases 

 neither side is sexually perfect. If the halves of such a gynan- 

 dromorph came apart, perhaps one would be a free-martin. 



The behaviour of homologous twinning in heredity has been 

 little studied. It does not exist as a normal feature in any animal 

 which is amenable to experiment, and we cannot positively 

 assert that a comparable phenomenon exists in plants; for in 

 them — the Orange, for example — polyembryony may evidently 

 be produced by a parthenogenetic development of nucellar tissue. 

 It is possible that in Man twinning is due to a peculiarity of the 

 mother, not of the father. It may and not rarely does descend 

 from mother to daughter, but whether it can be passed on 

 through a male generation to a daughter again, there is not 

 sufficient evidence to show. The facts as far as they go are 

 consistent with the inference which may be drawn from Loeb's 

 experiment, that the twinning of a fertilized ovum may be de- 

 termined not by the germ-cells which united to form it, but by 

 the environment in which it begins to develop. The opinion that 

 twinning may descend through the male directly has been lately 

 expressed by Dr. J. Oliver in the Eugenics Review (191 2), on the 

 evidence of cases in which twins had occurred among the rela- 

 tions of fathers of twins, but I do not know of any comprehen- 

 sive collection of evidence bearing on the subject. 



Besides twinning of the whole body a comparable duplicity 



