Manchester Memoirs, Vol. Ixii. (19 17), No. 2 5 



In Hydatina senta there are two 'kinds of females, those which 

 parthenogenetically produce other females with a similar method 

 of reproduction, and females 'which produce males in the same 

 way. These females are also capable of being fertilised. The prob- 

 lem is to discover what are the factors concerned with the 

 appearance of these various forms. 



Maupas connected the variation with differences in tempera- 

 ture, and Nussbaum with variations in nutrition, but the results 

 they obtained were not very conclusive. Punnett worked on a 

 strain which had proved to be entirely female producing and 

 subjected it to temperature variations. The rate of reproduc- 

 tion was reduced, but no male-producing females developed. The 

 same result was obtained by feeding experiments. He therefore 

 concluded that temperature and nutrition have no effect on male 

 production and that it Is the property of certain females to 

 produce male-producing females in a definite ratio; and also 

 that the differences between the females were due to variations 

 in the character of the gametes which united to form the resting 

 egg from which each strain sprang. 



Recently extensive experiments have been made by two 

 American zoologists, Whitney and ( Shull. Shull in 1910 came to 

 the conclusion that neither temperature nor starvation had any 

 effect, but that the chemical content of the water in which the 

 animals lived was the decisive agent in the production of males. 



A solution of horse manure was sufficient entirely to prevent 

 the appearance of males, and identical results were obtained 

 after the solution had been boiled or dried and redissolved. The 

 substance in the solution which effected the result was found also 

 to be insoluble in ether or absolute alcohol. 



The alkalinity of the water was also tested. A solution of 



N 



— NaOH was diluted with ten times its own volume of spring 



10 



water, which was slightly alkaline : a second solution of the same 



substance was also diluted 'with forty times its own volume. The 



result of the experiment, controls being used the whole time, was 



that the greater the alkalinity the fewer males were produced. 



This lowering in the number of males was also observed with a 



weak solution of urea. 



Solutions of ammonium chloride, ammonium nitrate, and 



M 



ammonium hydroxide in the strength of , all caused the pro- 



500 



portion of males to be reduced! to one half the normal number. 



A further paper was published by Shull and Ladoff in 191 6, 

 in which it was shown that oxygen in the water increased male 

 production. 



