NOTES ON A 32 MILLIMETER FREEMARTIN

¹ TRINITY COLLEGE, HARTFORD, CONN., AND MARINE BIOLOGICAL LABORATORY, WOODS HOLE, MASSACHUSETTS

1. A 32 mm. freemartin twin to a 34 mm. male is compared with a normal female of like size as to reproductive organs, and with normal male as to gonad.

2. It differs from the female control in having a thinner secondary sexcord region and thinner müllerian duct, lacking lumen in places where the control has one. Nevertheless it is more like the female than any other freemartins with vascular anastomosis so far studied.

3. Placental vascular anastomosis between the twins was very slight—hardly more than capillary—and the placentæ pulled apart with slight bleeding. So it permitted very limited transfusion of male hormone, a situation correlated with slight modification from female type shown in small gonad and thin ovarian cortex and müllerian duct.

4. Comparison with other freemartins as to placental and sexual conditions indicates a blood-borne hormone as the agent rather than an "organizer" found effective in early amphibian differentiation. Mere tissue cohesion fails to condition the modifications as it does in Spemann's transplants.

5. Comparison with other gonads figured for freemartins and with new material indicates that some formerly anomalous regions in older freemartin gonads are derived from secondary sexcord remnants which failed to be resorbed and that these cortical regions frequently develop in freemartins to some degree and may or may not disappear.

6. This study adds support to the theory of the freemartin of Lillie and Keller and Tandler, that it is female, normally determined zygotically, but abnormally differentiated sexually by the intervention of a male hormone received from her twin brother in utero.