No. 637] SHOFTER ABTICLES AND DISCUSSION 181 



Platygaster; 73 from the carcasses of Fhopalomyia and 128 from 

 those of Walshomyia. The remarkable character of the sex 

 ratios, as revealed in the published data, is emphasized by the 

 additional facts secured from the more recent rearings. It 

 therefore seems worth while to publish the full data, which is 

 given in condensed form in the following table. In the first 

 column the total number of individuals in each brood is given ; 

 in the second, the number of females; and in the third, the 

 number of males. In the fourth column are listed the number 

 of broods showing the combination of females and males in the 

 corresponding horizontal line. 



The total number of individuals in the 200 broods is 2,722, of 

 which 2,346 are females and 376 males. The average per brood 

 is 13.61. The size of the brood reared from Walshomyia is very- 

 much smaller than those from Bhopalomym. There are 1,417 

 individuals in the 128 broods from Walshomyia, or an average 

 of 11.07 per brood. The broods from Rhopalomyia have 1,305 

 individuals, or an average of 18,12 per brood. This represents, 

 an average increase of 63.6 per cent. The rate of increase in 

 the number of males per brood from Walshomyia to Rhopalo- 

 myia is almost the same as this. The average number of males 

 in broods from Walshomyia is 1.55, and in those from Rhopalo- 

 myia is 2.45. This represents an increase of 58 per cent. 



The difference in the size of broods is, in all probability, due 

 to tlie difference in the size of the two host larvEe. The larva of 

 Wiopalomyia is almost twice as large as that of Walshomyia, 

 iiiid Ihmii'o (iiiist fiirnisli a more abundant food supply for the 

 mult i|.li,-ai ion of cmhryos at tlie time of their formation in the 



One of the most striking facts in the data is the preponder- 

 ances of females. Approximately 86 per cent, of the individuals 

 are females. No male brood has been found, and in not a single 

 instance does the numher of males exceed or even equal the 

 number of females in a brood. There are, however, nine pure 

 female broods. Of the 191 mixed broods 113, or 59.61 per cent., 

 have a single male present in each brood. The other 78 broods 

 show the following numbers of males: Thirty with two males 

 each; twenty-four with three eacli ; ten with four each; four 

 with five each; four with six fai-li : thi-tu' with seven each; two 

 with eight each; and one with \on. 



Another interesting fact is the fro.inriit occurrence of broods 

 with a single male. Almost sixty pin- cent, of the mixed broods 



