ZOOLOGY: F. R. LILLIE 
467 
both with reference to the time of origin and the extent of the vascular 
anastomosis. 
We have hitherto noted only that the free-martin is sterile whenever 
blood-community with its male twin exists during foetal life, i.e., in 
about seven-eighths of all cases, and that otherwise it is normal. What 
is the nature of this steriHty? Observers from the time of John Hunter' 
(1786), who have studied the anatomy of free-martins, have all noted 
the intersexual character of its reproductive system — the internal 
organs of reproduction are largely male in type, the external female — ■ 
and the later students of the free-martin have generally regarded it as a 
modified male on account of the character of the internal organs and for 
other reasons (Spiegelberg,^ D. Berry Hart,^ Bateson,*^ Cole^). The 
gonad is sometimes absent or exceedingly rudimentary, but when well 
developed it never exhibits any trace of ovarian cortex, and its structure 
is testis-like, though germ-cells are not formed. The sexual ducts 
show reduction or absence of the female parts and a graded series of 
development of the vas deferens. The external parts are usually typical- 
ly female. We have on the one hand, therefore, failure of development 
of the internal female reproductive organs, and, on the other hand, the 
male parts, which usually degenerate, undergo development. Anatomi- 
cally the free-martin is definitely intersexual, to a variable extent as will 
be seen. 
The writer has studied the anatomy of 22 foetal free-martins ranging 
in size from 7.5 to 28 cm. The striking results of this examination were 
(1) The gonads remain rudimentary in size during this period; (2) the 
female ducts fail to develop; they frequently remain in part as un- 
developed rudiments, but in other cases disappear as completely as in the 
male. (3) The male ducts develop in varying degrees, always more 
than in the normal female, though rarely to the same extent as in the 
male. (4) Gubernacula invariably developed in the free-martins 
and formed peritoneal evaginations exactly as in males. (5) In one of 
the oldest foetuses the gonads had entered the saccus vaginaHs as in the 
male. (6) In my material the external organs were always typically 
female. 
Miss Chapin^ made a histological investigation of the gonads of the foetal 
free-martin under my direction and determined that the ovarian cortex 
never forms, but that a quite typical albuginea develops over the sur- 
face as in the testis of the male. The medullary cords, homologue of 
the seminiferous tubules of the male, also underwent unusually great 
development. 
A seven weeks old free-martin examined by the writer possessed testes 
