June, 19-14] LuTz: Drosophila Ampelophila. 135 



doubt a relation between certain somatic characters and the sex 

 chromosome. These " sex-linked " characters are not secondary 

 sexual characters but it is probable that this fly may help us to an 

 understanding of the latter since there seems to be a relation, possibly 

 indirect, between the two.^ 



The species also offers an excellent opportunity to study those 

 problems which we, curiously enough, term " biological." In nature 

 it feeds on all sorts of fermenting material and has been reared even 

 from human excrement. In the laboratory the most convenient and 

 satisfactory food is over-ripe banana. It is difficult to say just how 

 many eggs are laid by each female but the average is probably two or 

 three hundred. Fig. 491 in Packard's (1898) Text Book of Ento- 

 mology shows the pair of filaments with which the eggs are provided. 

 In oviposition the end of the egg bearing these is the last to leave the 

 oviduct and they protrude from the fermenting mass in which the egg 

 is usually laid, probably serving a respiratory function. 



It sometimes happens that the egg hatches before it leaves the 

 female. As this does not usually occur unless no suitable material 

 in which to oviposit has been found it is improbable that any of the 

 oviviviparous offspring ever reach maturity. The longest period at 

 normal temperatures required for hatching that I have observed is 

 about fifty hours. The average is probably less than thirty. Such 

 observations are difficult to make with large numbers and I have 

 combined the egg and the larval stages in most of my work. 



The larvae usually feed near the surface of the fermenting mass. 

 I have reared the fly for several generations in a glass of stale beer. 

 In this case the larvae were able to keep a position just under the 

 surface film where it met the glass. The length of the larval period 

 varies greatly according to temperature, food supply and other 

 conditions. The accompanying table gives the result of an experi- 

 ment involving about 4,000 flies fed on banana at a fairly constant 

 temperature approximating 25° C. Pupation began four days after 

 egg-laying and came on with a rush during the fifth and sixth days; 

 then the number gradually dropped off until the four individuals 

 which required eleven days. There is little or no sexual dift'erence, 



1 Lutz, F. E., 1913, "Experiments Concerning the Sexual Difference in the 

 Wing Length of Drosophila ampelophila," Journal of Experimental Zoology, 

 XIV, pp. 267-273. 



