GERM-CELL HISTORY IN THE BROOK LAMPREY 103 



Banta draws the conclusion from his observations that sex 

 depends on environmental factors which influence the general 

 physiological whole of the organism. In the intergrades the 

 sexual balance has in some way been disturbed and the origin 

 of this disturbance he considers a mutation. 



g. Hermaphroditism as a result of hormone action. Another 

 interesting case of disturbed sexual condition is found in the so- 

 called free-martin in cattle. Frank Lillie ('16, '17) has made a 

 study of this problem. Forty-one cases of twins were examined 

 in utero and a classification made of them without a possibility 

 of error. In fourteen cases both members were males, in six 

 cases both were females, and in twenty-one cases the two were of 

 opposite sex; 97.5 per cent were monochorial, but, in spite of this, 

 nearly all were dizygotic as determined by the number of cor- 

 pora lutea present. It was found that twins in cattle are nearly 

 always the result of fertilization of an ovum from each ovary. 

 As development proceeds, the developing embryos sink down 

 into the median portion of the uterus and the blood-vessels anas- 

 tomose in the chorion, so that it is possible to inject the blood- 

 vessels of either foetus from the other. If both of the embryos 

 are of the same sex, no harm results from the continuity of their 

 circulations; but if of different sex, the reproductive system of the 

 female is largely suppressed and certain male organs are devel- 

 oped. This is interpreted as a case of hormone action which 

 may be due to a more precocious development of the male hor- 

 mone or to its natural dominance. In this case, therefore, a dis- 

 tinction can be made between the effects of the sex-determining 

 factors that are zygotic and those due to hormones. But the 

 sex reversal is not complete and the result is the development of 

 an intersexual individual. 



h. Hermaphroditism as the result of parasitism. That a par- 

 tial reversal of sex may be induced by parasitism has been ob- 

 served by Geoffrey Smith ('10) in the case of the spider-crab, 

 Inachus, when infected with the rhizocephalan, Sacculina. The 

 males, under the influence of the parasite, are capable of assum- 

 ing all the female secondary sex characters, and often even develop 

 ova in the testes. In this case, however, the females do not seem 



