468 MISSES K. FOOT AND B. C. STKOBELL : 



" First. Dominance is absent in the Fi hyhrid generation.^^ — This is 

 supported by our measurements o£ the intromittent organ ; for not one 

 of the ten * Fi hybrids has a length of intromittent organ that comes within 

 the range characteristic of either variolarius or of servus. They are all 

 intermediate : one measures 109 mm.^ one 122 mm., two 124 mm., four 

 126 mm,, one 132 mm., and one 134 mm.f 



Absence of dominance is equally evident in the case of the genital spot ; 

 for nine of the eleven Fj hybrids are variable intermediates, while only two 

 are like one of the parent species — i. e., like servus in having no spot. 



" Second. Tlie F-^ hybrids are intermediate in size." — This is quite true for 

 both the intromittent organ and the genital spot, though it can be more 

 clearly demonstrated in the former. 



The mean length of the intromitt(mt organ of Fuschistus variolarius is 

 96-70 mm. (Table 1), and that of F. servus is 166-41 mm. (Table 2). A 

 precise intermediate between these two means would be 131*55 mm. (^. e., 

 34-85 mm. above the mean of F. variolarius or below the mean of E. servus). 



The mean length of the organ in the Fj hybrids computed from the ten 

 specimens is 124-9 mm., which is slightly below the precise intermediate 

 (131-55 mm.), and shows therefore a stronger inheritance from E. variolarius 

 than from E. servus. The exact length of each specimen, as stated above, 

 shows the Fi intromittent organs to be very variable intermediates, ranging 

 between 109 mm. and 134 mm. in length. 



In the case of the genital spot the slightly stronger inheritance is from 

 E. servus instead of from E. variolarius, for two of the eleven hybrids are 

 like servus in having no spot. The remaining nine specimens are variable 

 intermediates (photos 8 to 14, Plate 28 of this volume), and therefore the 

 genital spot as well as the intromittent organ may be said to be approximately 

 intermediate in size between the two parent species. 



" Third. Mendelian segregation is absent in the F^ hybrid generation." — 

 In our study of the transmission of the genital spot of variolarius (Foot and 

 Strobell, '14 a) we divided the hybrids into three groups — those having 

 a genital spot like those of pure variolarius, those without a spot like servus, 

 and those with a spot intermediate between these two extremes. In the case 

 of the intromittent organ we have grouped the hybrids into three similar 

 classes — those having a length of intromittent organ within the range of that 

 of variolarius, those with a length of organ within the range of that of 

 servus, and those with a length intermediate between the longest found 

 in variolarius and the shortest found in servus. 



If we are looking for a simple Mendelian segregation of 1-2-1 and assume 

 that the heterozygotes are represented by the intermediates, we should 



* The iutromittent organ of the eleventh F^ hybrid was destroyed in dissection, 

 t These lengths are given in connection with each photograph (7 to 14), and can therefore 

 be compared with the inheritance of the genital spot. 



