Chromosomes in Parthogenetic and Sexual Eggs. 161 



From a Mendelian point of view, two classes of broods are 

 expected, if the absent type be the dominant and the present type 

 (specks). The recessive offspring of a pair should be either all 

 without (DD X DD or DD X DR), or 3 absent to 1 present 

 (DR X DR). Two groups, in fact, appear; but when the specks 

 occur, the number of individuals having them departs far from 

 expectation in many cases. 



When a fly with specks present is bred to one with specks 

 absent the Mendelian expectation is either all with specks present 

 (DD X RR) or half with and half without (DR X RR). The 

 following cases show considerable departures from expectation. 



Absent. Present. 

 28 o 



48 56 



63 3 

 65 o 



The second generation of the last combinations when 100 per cent, 

 absent was obtained, should give the 3 to 1 proportion. 



Several other mutants of these flies are under observation. A 

 male in which the red pigment of the eye is totally absent has 

 produced in the first generation, by his sisters, 162 red eyed to one 

 white eyed fly. The results show that the character is germinal, 

 but reappears at present in only a very small percentage of the 

 first generation. 



103 (513) 



The chromosomes in the parthenogenetic and sexual eggs of 

 phylloxerans and aphids. 



By T. H. MORGAN. 



[From the Department of Zoology, Columbia University.] 



An examination of the ovarian parthenogenetic and sexual 

 eggs of aphids and phylloxerans has shown that the synapsis stage 

 is entirely omitted in the parthenogenetic eggs, both male- and 

 female-producing; while on the other hand the sexual eggs pass 

 through a synapsis period, i. e., a period when the chromosomes 

 contract to one side of the nucleus reappearing later in the re- 

 duced number. These observations show that the full number of 



