I4« ESSAYS OF A BIOLOGIST 



chromosomes may be altered in certain crosses, and 

 that this altered balance in the constitution is reflected 

 in some cases in a state permanently intermediate 

 between male and female, in others by a reversal of 

 sex at some point during development. For various 

 reasons we should not usually expect reversal in 

 mammals ; but if such abnormal balance should 

 exist in the constitution, as it well might, we should 

 expect a gonad secreting an abnormal, intermediate 

 secretion. This we might also expect as the result 

 of certain accidents of embryonic life, as actually 

 happens in the abnormal female cattle known to 

 formers as free-martins. These animals are always 

 born co-twin to a male, and their abnormality is due to 

 the blood-systems of the embryonic membranes of the 

 twins having fused, so that the secretion of the develop- 

 ing male's gonad acts upon the developing female. 



Further light on abnormally-directed sex-instinct 

 is thrown by recent analysis of abnormal domestic 

 animals by Crew.^ In both goats and swine he finds 

 that by far the commonest form of sexual abnormality 

 is one in which the external appearance, at least in 

 youth, is so nearly female as to raise no question in 

 the mind of the casual observer ; about the time of 

 maturity, however, male secondary sex characters 

 begin to develop, including male instincts ; and dis- 

 section reveals the presence of a double set of ducts 

 — ^the female uterus and vagina, the male epididymis 



^ Crew, '23. 



