CKOSSING EUSCHISTUS VARIOLAKIUS AND EUSCHISTUS SERVUS. 353 



with their own species. This may indicate that possibly the factor of 

 selection may be in part responsible for some of the failures of our breedino- 

 experiments. 



We raised only 10 cJ and 22 ? from the one pair of yonnor variolarius 

 that mated in the laboratory in 1912. We undoubtedly would have had 

 more, but the femnle was fertilized only once, as we transferred this male to 

 the Fi hybrid females^ as described above. This variolarius female deposited 

 58 eggs from August 17th to September 7th, and 36 of these hatched, 32 being- 

 reared to the winged stage (10 c? & 22 ? ). The Fi hybrid female that was 

 fertilized by this same male deposited 119 eggs and 36 hatched. 



The males from these two females were photographed and ai'e shown on 

 Plate 34. Photos 59 to 61 show the males from the pure variolarious pair, 

 and photos 61 to 66 show the males from the F^ hybrid female and the pure 

 variolarius male. 



These photographs demonstrate that the spot is inherited through the pure 

 variolarius fern de (photos 59 to 61) more intensely than it is throuo-h the 

 Fi hybrid female (photos 62 to 66), and a comparison of photos 62 to 66 

 with those when both parents are Fi hybrids, Plates 29-33, demonstrates 

 that the spot is transmitted through a pure male variolarius much more 

 strongly than through an Fi hybrid male. All such facts bearing on the 

 inheritance of the genital spot are important in testing modern chromosome 

 theories of sex-determination in the light of the transmission of this exclusively 

 male character. 



Discussion. 



Any analysis of the results of cross-breeding ex[)eriments involves a 

 discussion of their bearing on fundamental problems of heredity, and we 

 should examine the tacts demonstrated by our recent experiments in the 

 light of the popular theories which claim to offer a partial solution of some 

 of the important problems of heredity. The hypothesis of first interest to 

 the cytologist is the one that claims to otler an explanation of the trans- 

 mission of characters by the assumption that the factors essential to their 

 transmission are carried and distributed by definite chromosomes, but a 

 discussion of our results from this point of view is reserved for a paper in 

 which the cytological phenomena can be fully demonstrated by photooraphs. 

 A brief statement of the facts and their bearing on recent chromosome 

 theories was given in the preliminary report of our work (^13). 



In the present paper we shall merely restate the facts and conclusions in 

 order to present the evidence in detail, as it is demonstrated in the photo- 

 graphs of Plates 28-34. 



First. The results demonstrate that an exclusively male character (the 

 genital spot) can be inherited without the aid of the Y chromosome. This is 



