114 



those experiments not more than 15 per cent, of the transfers were made 

 before the tenth day. A census ^^■as taken of the parents practically every 

 day. In a few cases five days may have elapsed before a record was 

 entered. In case a fly was dead the sex was noted and recorded. 



This record, then, includes the length of life of the relatively long-lived 

 Inbred stock ; the short-lived Ti-uncate stock ; tlie liybrid offspring between 

 the two stocks and the life of tlie grandchildren. 



2. Analysis or the Data. 



The curves which follow are plotted from the life records of 898 flies 

 which are recorded in Part I and Part II of my Studies on "'Fertility and 

 Sterility in Drosophila (uiipelopliihi."* The length of life is expressed in 

 days and is indicated by the abscissa, while the number of individuals is 

 in each case expressed by the ordinate. 



Curve A shows the distrilyution of the mortality of the Inbred stock. 

 The curve is drawn from the records of 1'.>1 individuals. The average life 

 of this lot is 37.4 days. The 94 males lived an average of 40.5 days; 97 

 females lived an average of 34.5 days. The males lived sis days longer than 

 the females. 



Curve B shows the distribution of mortality of the 272 Truncates, the 

 average life of which was 21.4 days. The 9(i males averaged 2G.9 days; the 

 176 females 18.5 days. The males of this stock lived 8.4 days longer than 

 the females. It is to be noted that the flies of this stock live approximately 

 lialf as long as those of the Inbred stock. 



The hybrid that results from crossing the Truncate aiad Inbred stocks 

 lives longer than either parent, as is brought out in curve C. For, while 

 the jtarents live 21.4 and 37.4, I'espectively, the offsiu-ing from the cross live 

 47 days. This record is based on 42 flies. Thirteen males lived 47.8 days, 

 while 29 females lived 46.4 days. The datn is too small to base any .safe 

 conclusion in regard to any difference that may exist in the length of life 

 between the male and the female. That the hybrid lives longer than either 

 l)arent is also liorne out by ciirNc (", where a partial record is given 

 of 218 flies, 'i'lic cxiieriniciit was discoiitiniu'd after tliirty days, at 

 the end of which time it was found tliat only 19 per cent, of the flies had 

 died. The mortality in this case corresponds f.-iirly well with the mortality 

 in the case as shown in tlic cnrvc (". in wliich seven in 12 died within the 

 first thirty day.s, a nnnfality of 11 per cent. 



■Journal of lOxpcriiiiunlal Zooloiry, 1911. \<.l. WII. Xos. 1 and 2. 



