358 SUMMARY OF CURRENT RESEARCHES RELATING TO 



one paternal component. Before every cell division the members ol 

 each pair become so intimately united that they may be said to 

 conjugate. 



Sterility in Drosophila ampelophila.* — Roscoe R. Hyd< has 

 studied a kind of sterility affecting the female insect, and finds thai it 

 bears no relation to a low fertility. The kind of sterility which was 

 studied is due to some defect, probably in the oviduct of the female, so 

 that she is unable to' deposit her eggs. The defect is transmissible 

 through inheritance by at least some of the brothers and sisters of the 

 affected females when mated to a fertile race, to the grandchildn n. but 

 apparently not to the sons, or daughters, or grandsons. It is then 1 

 recessive and affects females only. 



The process of inbreeding brother- and sisters cannot be held to 

 r> sponsible for the condition, but probably serves to bring it out when 

 latent in a strain by making the necessary combinations. The charactei 

 seems amenable to selection, and can be made to affect fully 50 p.c. of 

 the females, or can be practically eliminated by making the proper 

 selections. 



It seems very probable that sterility as it affects the male bears no 

 causal relation with sterility as it appears in the female. The defect in 

 the female behaves after the manner of a Mendelian character, in that 

 it reappears after skipping a generation. The normal function is 

 dominant to the negative condition. An unaffected male can transmit 

 something as a dominant character which ensures the normal egg- 

 deposition in his daughters. The defect is sex-limited in the sense that 

 it affects the female only. 



Sex-linked Lethal Factors in Drosophila. f--T. H. Morgan has 



experimented in reference to lethal factors in this fly and their influence 

 on the sex-ratio. The nature of the inquiry may be stated. A 

 recessive lethal factor is one that brings about the death of the indi- 

 vidual in which it occurs, provided its effect is not counteracted by the 

 action of its normal allelomorph. The term is not intended to mean 

 that some poison is produced that destroys the individual, but rather 

 some heritable defect that renders the individual unable to live. Lethal 

 factors may be sex-linked or not, i.e. they may lie carried by the sex- 

 chromosome or by an autosome. If the lethal factor is sex-linked it 

 will kill any male in which it occurs, since the male has but one 

 X-chromosome. Such a factor, therefore, cannot be transmitted 

 through the male line, or transferred from one lethal stock to another 

 lethal stock. If two sex-linked lethals should ever occur in the same 

 female, one must have arisen as a mutation independently of the other. 



Fertility in Drosophila. J — Roscoe II. Hyde lias studied a " truncate '" 

 stock of Drosophila ampelophila, differing from the wild stock in having 

 the ends of the wing squared instead of rounded, in having a duration 



* Jouru. Exper. Zool., xvii. (19141 pp. 141-71. 



t Jouru. Exper. Zool., xvii. (1914) pp. 81-122 (7 figs). 



j Journ. Exper. Zool. xvii. (1914) pp. 173-212 (9 figs.). 



