234 
Proceedings of the Royal Society of Edinburgh. [Sess. 
which causes the anomaly does not as yet seem to have been 
observed in simple born calves. One finds, however, sometimes 
in such cases incomplete organs in a male. 
The conclusion stated under (4) is the most novel, as it points to a free 
martin with a sound female twin. It is of great interest theoretically in 
regard to Mendelism in this connection. The necessary modification of (1) 
will be seen presently. 
As Hunter’s specimens are still in the Museum of the Royal College of 
Surgeons, London, it was therefore a matter of great interest that the 
sexual glands should be examined microscopically. This has just been done 
under the direction of Dr Arthur Keith, the Curator, and by permission of 
the Council ; and I am greatly indebted to Dr Keith for permission to 
examine the slides and make microphotographs. I was able also to see the 
naked-eye specimens themselves during- a visit I paid to the museum. 
These specimens, although now about 140 years old, are in perfect pre- 
servation, and it is still more remarkable that the microscopical sections, 
cut in celloidin and stained with logwood and eosin, show even the finer 
details in a recognisable manner. 
The special fact that emerges is that all the sexual glands are testes in 
Hunter’s cases, that adjacent structures are epididymis, and that in none of 
the sexual glands are ova present. The characteristic testicular tissue is in 
the form of tubuli seminiferi, and in only one are spermatozoa present. 
They thus show the condition usually found in undescended testes in man 
and in the testis normally before descent is complete. I add a report of 
Hunter’s specimens, and the structures are illustrated in the figures given. 
The examination of the slides prepared from John Hunter’s free- 
martin specimens gave the following results : — 
Slide 678, testes with tubuli seminiferi; 682, epididymis; 686, epididymis and 
testes; 688, epididymis; 689, testes and hydatid testis (Mullerian); 690, testes; 
691, testes and hydatid testis; 692, testes (Arbuthnot) ; 693, testes (Wright); 694, 
testes, scanty elements. In 691 the Miillerian hydatid is well shown (vide figs. 
3 and 4, PI. II.). 
It seems to me, therefore, fully established that the free-martin, when 
the co-twin is a potent male, is a sterile male, and not a sterile female, i.e. 
they are identical male twins except in their genital tract and secondary 
sexual characters. 
The following table shows the main cases (thirty in number) I have 
been able to collect. 
