400 Phylum Arthropoda 



incubator in front of an electric fan which is in continuous operation. 

 Under these conditions, the life cycle of 5. coprophila occupies about a 

 month, divided approximately as follows: egg stage, 5-6 days; larva, 

 14-15 days; pupa, 3-4 days; adult, 5-8 days. Thus 12 to 14 successive 

 generations may be grown in the course of a year. 



Breeding Technique. The type of inheritance found in Sciara copro- 

 phila necessitates a technique somewhat different from that employed 

 with other organisms. In this species individual females typically give 

 "unisexual" progenies. Occasionally there will be one or more "excep- 

 tional" males in a female progeny, or "exceptional" females in a male 

 progeny, in which case sib matings may be made; but usually such 

 inbreeding is not possible. It is advisable to cross the various strains 

 with each other frequently to keep the stocks in good condition. 



The technique outlined above has been found reasonably satisfactory 

 for a few other species of Sciara, but since different species may differ 

 both in respect to food habits and to sex ratios it is necessary to modify 

 the methods to fit the needs of individual cases. S. pauciseta and 5. 

 impatiens are both vigorous species and may probably be reared satis- 

 factorily by this same method. 



CULTURE OF SCIARA 



F. H. Butt, Cornell University 



SCIARA females were caught from cabbages, corn, potatoes, and 

 onions, and placed in quart-size wide-mouthed Mason fruit jars 

 containing 1 inch of agar covered with % mcn °f bran, wheat flakes, or 

 other such breakfast food; % inch of sheep manure; and 2 inches of 

 wet sphagnum that had been sterilized by heating for 20 minutes to 

 rid it of mites. The flies laid eggs readily in the sphagnum, the next 

 generation multiplying in enormous numbers. The life cycle on the 

 average was 26 days at room temperature, although it lengthened during 

 the winter months. The food contained in the medium was sufficient for 

 one generation only. Another generation of larvae, if allowed to develop 

 in the same jar as the first, always appeared stunted and greatly depleted 

 in numbers. Therefore new jars should be made up for each genera- 

 tion. 



To obtain eggs for embryological work, 50 to 100 females were col- 

 lected from the breeding jar and put in a cage which consisted of a 

 lantern chimney covered with a piece of muslin, resting on a piece of 

 cheesecloth placed on black paper. The whole cage was placed on damp 

 sand which kept the paper and cheesecloth moist. This method pre- 

 vented the eggs from drying out. Eggs were collected at intervals and 

 placed in salve boxes in the bottom of which had been placed pieces of 



