338 KATHARINE FOOT AND E. C. STROBELL. 



PLATE I. 



PHOTO i. Intromittent organ of Euschislus variolarius the father of the 

 E. variolarius female that was fertilized by the pure E. ictericus male. 



Length of intromittent organ 96 mm. 



PHOTOS 2, 3 and 4. Intromittent organs of three brothers of the E. variolarius 

 female that was fertilized by the pure E. ictericus male. From this cross we raised 

 the Fi female which was back-crossed with a pure E. ictericus rriale and produced 

 the offspring described in this paper. 



Length of the intromittent organ of photo 2, 100 mm. of photo 3, 94 mm. 

 of photo 4, 99 mm. 



PHOTOS 5 to 8. Typical specimens of the intromittent organ of Euschistus 

 variolarius. 



Length of the intromittent organ of photo 5, 93 mm. of photo 6, 93.5 mm. 

 of photo 7, 97.5 mm. of photo 8, 98 mm. 



PHOTO 9. Intromittent organ of the Euschistus ictericus of the original cross 

 (cage 5, p. 324). This male ictericus was raised in our laboratory and fertilized 

 the Euschislus variolarius female from which we obtained the Fi female used for 

 our back-cross experiment. 



Length of the intromittent organ 60 mm. 



PHOTO 10. Intromittent organ of the Euschistus ictericus that fertilized the Fi 

 female . . . (the father of all the offspring from our back-cross experiment). (See 

 record, p. 326.) 



Length of the intromittent organ 63 mm. 



PHOTOS 11, 12 and 13. Intromittent organs of three of the original stock of 

 Euschistus ictericus that we received from Washington, D. C., May 18, 1911. 



Length of the intromittent organ of photo 11, 62 mm. of photo 12, 60 mm. 

 of photo 13, 62.5 mm. 



PHOTO 14. Intromittent organ of an E. ictericus male that was raised in our 

 laboratory in 1911, kept through the winter, and in 1912 mated with a pure E. 

 variolarius female. (See account of cage 12, p. 325.) 



Length of the intromittent organ 60 mm. 



PHOTO 15. Intromittent organ from one of the brothers of the E. ictericus 

 that was used for the original cross with E. variolarius. These were raised in our 

 laboratory in 1911. 



Length of the intromittent organ 54.5 mm. 



PHOTOS 16 to 20. Intromittent organs from five typical E. ictericus males 

 that were raised in our laboratory during the summer of 1911. 



Length of the intromittent organ of photo 16, 58 mm. of photo 17, 59 mm. 

 of photo 18, 60 mm. of photo 19, 61 mm. of photo 20, 64.5 mm. 



