2l6 RAYMOND PEARL AND H. M. PARSHLEY. 



"Das Ei, welches, wenn es befruchtet wird, noch nicht einen 

 gewissen Grad der Reifung erreicht hat, giebt ein Weibchen; ist 

 dieser Grad der Reifung iiberschritten, so giebt das Ei, wenn es 

 befruchtet wird, ein Mannchen. 



"Wenn zur Zeit der Brunst, ein einziges Ei, vom Eierstock 

 abgelost, langsam durch den Geschlechtsapparat herabsteigt 

 (Thiere, welche ein Junges gebaren), so geniigt, es dass die 

 Befruchtung am Anfange der Brunst statthabe, um Weibchen zu 

 zeugen, und am Ende, um Mannchen zu zeugen, indem die 

 Umwandlung (vire) des Zustandes des Eies normal wahrend der 

 Dauer seines Durchganges durch den Geschlechtskanal statt- 

 findet." 



Curiously enough this theory, while exciting much interest 

 at the time of its appearance, has never been given any adequate 

 experimental-statistical test. The only experimental evidence 

 which Thury himself offered in its favor was that obtained by a 

 friend Cornaz 1 which was so brilliantly confirmatory as to arouse 

 suspicion in the minds of all subsequent workers, with the result 

 that it has never been regarded as of any particular worth. 

 At the best it was ridiculously inadequate statistically. Cornaz 

 states that by following Thury's directions as to time of service 

 he obtained 22 female calves in unbroken succession. In 7 cases 

 he desired and obtained male calves, the service in these cases 

 being late in the heat. 



Diising (loc. cit.} discussed Thury's theory at great length, 

 and pointed out in the following words one of its obviously 

 great weaknesses (p. 16): "Indessen ist diese eigentliche Thury- 

 sche Theorie in sofern nicht richtig, als immer nur ein gewisser 

 Uberschuss des einen oder andern Geschlechtes erwartet werden 

 kann." Thury postulated complete determination. 



Later writers have dismissed Thury's theory with rather scant 

 consideration. Thus F. H. A. Marshall (loc. cit., p. 630) says: 

 'Thury claimed that he could regulate the sexes in cattle by 

 allowing coitus only at the beginning or at the end of oestrous 

 periods, . . . but other investigators have failed to establish 

 Thury's conclusions." Morgan 2 (p. 393) says: "Thury based 



1 Published as a part of Thury's paper (loc. cit.), pp. 17 and 18. 



2 Morgan, T. H., "Experimental Zoology," New York, 1907. 



