STRAINS IX HYDATIXA SI.MA. 21 7 



pre-ent evidence collected from observations extending over a 

 period of about three years and including 300-500 partheno- 



etic ^em-ration-, -hows very clearly that strains exist which 

 differ in their percenta^- of male-producing females. 



Moreover, tin- t\\o -ister strains A and B which developed 

 from the -amc fertili/ed egg differed in their longevity. Strain 

 /! died out from general exhaustion in the 384th partheiio-enetic 



ration, whik- -train .-1 is still alive in the 5041)1 partheno- 

 n< -ration, although in a very weak and exhausted con- 

 dition. 



Shull lia> compared Mime of the New York strains of Ilydntina 



; \\itli a -train from Baltimore and has found a divided 

 ilitlereiii in the rate of production of males in the tw Miain-. 

 II' 'It is safe to say, therefore, that we have lure t\\o 



pun- line- 1 1 1,1 1 1 1; -m one another in a fairly constant maim- i . 



and the din. is an internal one." 



SUMMARY. 



i. The prudiietioii of male-producing females can In- p.irtly 

 or \\holK i-epreNM-d hy external conditions in parthenogenetic 

 iai es ot Ily<!nlinn *i-nta. 



j. The jiartlu lie strains are shown to he distinct i 



cause mi'ltr identical external conditions they differ in their 

 po\\er t.. produi-i- male-producing females. This may indicate 

 that the\ differ in their potentiality of producing male-pn>ducin- 

 female- or that they differ in degree of respond cne to the 

 inllueiice- \\hich cause male-producing females to \n- ]>roducei|. 

 The latter alternative seems more probable. 



j. The tuo -i-ier parthenogenetic strains developing from one 

 fertili/ed egg dilh red in their longevity. One li\ed almut a year 

 longer and pro.lnced over one hundred IIIOR generations than 

 the other. 



1>I 'I ' ".li \l I \Hi>K.VTORY. 



WESLEYAN I'NIVERSITY. 

 MIDIM.KTOWN. CONN.. 

 January 3. 1912. 



