224 KATIIARIMC FOOT AND E. C. STROBELL. 



mission of this organ may justly be claimed as an index of the 

 method of transmission of the reproductive glands themselves. 

 Before giving these results we would express our great indebted- 

 ness to Professor Poulton and to Dr. Eltringham, of Oxford. We 

 are indebted to Professor Poulton for his kind response to our 

 wish to find an experienced entomologist in England who would 

 be willing to study E. variolarius and E. servus with the aim of 

 finding other characters than the genital spot that could be 

 studied in the hybrids. He kindly suggested Dr. Eltringham, of 

 Oxford, to whom we are indebted for the discovery that there 

 is a marked specific difference in the intromittent organ of E. 

 variolarius and E. servus. This discovery has made it possible 

 for us to secure the results which are recorded in this paper. 



RESULTS AND DISCUSSION. 



The intromittent organs of E. variolarius and E. servus differ 

 markedly in their length. We have dissected these organs from 

 the genital segment of many of the parent species, and from all 

 the hybrids, both of the FI and Fz generations. These have 

 been mounted and photographed at a magnification of 20 diam- 

 eters, and all have been carefully measured at this magnification. 

 The intromittent organ of E. variolarius varies in length between 

 85 5 and 106 mm., while that of E. servus varies between 146 and 

 182 mm. These measurements were made from 62 pure vario- 

 larius specimens, and from 62 pure servus specimens, the mean 

 length of the intromittent organ of variolarius being 96-5 mm., 

 and of servus 166-41 mm. 1 



Photos i to 4 show four typical intromittent organs .of E. 

 variolarius, these four varying in length between 94 mm. and 98-5 

 mm. Photos 5 to 8 show four typical intromittent organs from 

 E. servus, these four varying in length between 158 mm. and 182 

 mm. Photos 9 to 12 show four typical intromittent organs of 

 the FI generation derived from E. variolarius 9 X E. servus 

 cf . These four vary in length from 122 to 132 mm. We have 

 ten intromittent organs of this FI generation, nine of these 

 being variable intermediates, and one like pure variolarius. 



1 A discussion of the mean lengths of the hybrids and of the back-cross, and 

 their bearing on the Mendelian type of inheritance, will be given in a later and 

 more detailed report of these results. 



