CROSSING EUSCHISTUS VARIOLAEILTS AND EUSCHISTUS SEBVUS. 355 



spot, as the spot is never present in any o£ the females, neither in the pure 

 variolarins nor in the hybrids, although the fact that it is transmitted by the 

 female variolarins proves that the spot factors are present in the female, 

 though not expressed. 



Fifth. The results show that, although it is necessary to assume an 

 inhibitor only in the females of pure variolarins, in tlie hyhrids it becomes 

 necessary to assume an inJiibitor in the males also. The Fi hybrid males show 

 th© spot either very incompletely, or not at all, although they can transmit 

 the spot to the next genei'ation, and therefore they must carry the factors 

 necessary for its transmission, in spite of the fact that the appearance of the 

 spot in the Fi generation is partly or wholly inhibited. The two Fi 

 hybrid males of photo 7 have no spot * , the upper Fi male of photo 8 has 

 merely an indication of a spot and in the lower bug it is not much stronger. 

 The Fj males of photos 9 to 13 have a very insignificant spot, and the Fi 

 male of photo 14 has merely a trace of a spot, although the offspring of these 

 males frequently have a spot quite as pronounced as that of pure variolarins. 

 Compare these Fi males with one or more of the Fg males of photos 15, 

 28, 2G, 28, 32, 34, 35, 36, 40, 41, 46, 48, and 55. 



Sixth. The facts show that if we attempt to place this inhibitor in 

 definite chromosomes, we meet as serious difficulties as those involved in 

 assuming that the factors essential for the production of the genital spot are 

 carried by special chromosomes. In our preliminary report of these 

 experiments (''13), we discussed in full the evident results of placing this 

 inhibitor in various chromosomes : in the X chromosomes, in one of the 

 ordinary chromosomes, or in a pair of chromosomes, and vv© found that none 

 of these assumptions would accord with the facts. The facts force us to 

 regard these inhibitors as hypothetical forces which cannot logically be con- 

 fined to the chromosomes^ and are located we know not where — these hypo- 

 thetical inhibitors practically doing work that has been assigned to definite 

 chromosomes. As stated in the above-mentioned preliminary report, " the 

 facts force us to consign to these hypothetical inhibitors, not only the 

 responsibility of suppressing the spot factors in all the females, but also 

 of determining just how many spot factors shall find expression in the males 

 of the F] and Fg generations, and thus they practically relieve the chromo- 

 somes of the burden of unit distribution.'^ 



It would seem then that the facts are out of harmony with the theories 

 that offer an explanation of the transmission of characters on the assumption 

 that the factors essential to their transmission are carried and distributed by 

 definite chromosomes. 



* The two dark specks on the genital segment of the upper bug, close to the base of the 

 segment, must not be confused with the genital spot. In the lower bug a slight indication 

 of a spot can be seen with a lens, but it will probably not appear in the print. 



LINN. JOURN. — ZOOLOGY, VOL. XXXII. 30 



