240 Proceedings of the Royal Society of Edinburgh. [Sess. 
unequally divided by twinning (or otherwise in single cases), so that only 
recessive or non-potent genital determinants are allotted to the one twin, 
and in this way sterility is absolutely secured. 
On one point we have as yet no information, viz. as to whether or not 
the potent bull co-twin with the free-martin has its prostatic utricle 
normal. Theoretically it seems to me this may be defective or wanting, 
but here actual dissection is necessary. 
The free-martin is, according to Mendelian phraseology, a pure or 
extracted recessive qua its genital determinants, and the potent twin a pure 
or extracted dominant, both of F 2 in the Mendelian scheme. Occasionally, 
but very rarely, as in three of Numan’s cases, the recessive element is less 
complete. 
The potent bull alone can have offspring, and some of its males must 
breed true to the dominant genital determinants, in certain cases at any 
rate, as Mendel’s scheme demands and theory indicates. This will intro- 
duce a variation, i.e. we may get a bull not possessing a hydatid testis, 
and thus varying from the normal bull, and we get here one factor in the 
mechanism of variation ; but I defer the consideration of this.* 
According to J. A. H. Murray, the origin of the term “ free-martin ” is 
unknown. In Holland they are termed Kween, and in Brabant, Bouquetin ; 
in France, Taur; in ancient Rome, Taura was the term (Simpson and 
Spiegelberg). According to Simpson and others, the Romans did not seem 
to have been aware of the association of the “ Taura ” with twinning. 
I have to thank Professor J. Arthur Thomson for valuable references, 
and Mr Henderson for one undoubted specimen. 
LITERATURE. 
Allnatt, Bond. Med. Gaz ., vol. xviii., 1836, p. 528. 
Geddes and Thomson, The Evolution of Sex , 2nd edit., London, Walter Scott, 
1901. 
Gurlt, Lehrhudi der path. anat. Haussaugethiere , 1833, Tab. xxii. figs. 2-5. 
Hart, D. Berry, “ Mendelian Action on Differentiated Sex,” Abstract, Proc. 
Roy. Soc. of Edin., July 1909; Edin. Obstr. Trans., 1908-9, in extenso. 
Hering, Repert. der Thierheilh., 12 Jahrgang, 1851, p. 107. 
* Observations are still needed on such specimens. We need to know the exact con- 
dition of the organs in the potent animal, and this could best be done if such twin calves 
or specimens obtained in the cornua of slaughtered animals were examined as to details. 
Free-martins are not uncommon, but in Hunter’s days they were obtained from the farm 
and a history given ; now, in the -large sales where animals are bought, the history can 
seldom be obtained. 
