114 



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

 before the tenth day. A census was 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 : the hybrid offspring between 

 the two stocks and the life of the grandchildren. 



2. Analysis of the Data. 



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

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

 Sterility in DroHopliUa ampelophUit:'* The length of life is expressed in 

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

 in each case exjire^sed by the ordinate. 



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

 The curve is drawn from the records n\^ I'.il iiulividuals. The average life 

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

 females lived an average of 34.5 days. Tlie males lived six days longer than 

 the females. 



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

 average life of which was 21.4 days. Tlic 9(; uiales averaged 26.9 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 

 half as long as those of the Inbred stock. 



The hybrid that results from crossing the Truncate and Inbred stocks 

 lives longer tiian cither parent, as is lirought out in curve (". For, while 

 the parents live 21.1 ami .■'.7.4. I'espectively. the ol't'spriim from the cross live 

 47 days, 'i'liis record is based on 42 Hies. 'I'hirteen imiies lived 47.S days, 

 while 29 females lived 46.4 days. The data 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 tlie hyl)rid lives longer than either 

 parent is also l)orne out by curve C wlicre a partial record is given 

 of 218 flies. The experiment was discontinued after tliirty days, at 

 the end of wlii<-h time it was found that only 19 per cent, of the flies had 

 died. The mortality in this case corresponds fairly well with the mortality 

 in the case as shown in the curve C, in wliicb seven in 42 died within the 

 first thirty days, a mortality of 17 per cent. 



•Journal of Kxporiinonliil Zooloaiy, 191-1. \r)l. XVII, Nos. 1 and 2. 



