38 



MISCELLANEOUS PAPERS. 



picking- niig-ht be of consexjuence, although I realize that in most cases 

 such procedure would not be practicable. In order to demonstrate 

 what could be done in the way of gathering eggs of this species, on 

 the morning of Jul}^ 17 I went out in a small rowboat and collected 

 for an hour. At the end of this time a count showed 433 masses, and 

 an average of 250 specimens to each mass — a result obtained by count- 

 ing several and striking the average — gives a total of 108,250 single 



eggs taken as a result of the hour's work. 

 Eggs laid from 8.1:5 to 9.30 o'clock on 

 the morning of July 13 hatched before noon 

 of July 19, thus making the incubation 

 period six days in length. This is the 

 shortest incubation period I have observed 

 for any of the species of the family. 



In a previous paper I suggested that ker- 

 osene might be of consecpience if used on 

 the surface of stagnant water over which 

 eggs are in place, in order that the larvas 

 when they hatch and drop to the water 

 must pass through a tilm of the oil. Data 

 on this point are very ditiicult to obtain in 

 the natui'al Ijreeding grounds of the flies, 

 for it is almost impossible to find the very 

 small larvie after they have dropped from 

 the eggs and have become more or less 

 scattered among the debris which is usually 

 plentiful in these ])laces. 1 undertook to 

 test the matter by the use of a tank of 

 water on the surface of which kerosene 

 was placed at the rate of half a pint to each 

 sfjuare yard of surface. Spharganium 

 leaves to which eggs were attached were 

 brought in from the marsh and put into a 

 ))ottle, as one would arrange a bouquet, and 

 this placed on the bottom of the tank so 

 that the parts of the leaves to which the 

 eggs were attached were a foot or more 

 above the surface of the water which con- 

 tained the layer of kerosene. Even under 

 these conditions an exact count could not 

 be obtained, because the kerosene appeared to affect different speci- 

 mens differently. Some were killed very quickly, some died after an 

 hour or more, while others did not appear to suffer particular incon- 

 venience from the treatment. Further observation is necessary in 

 order to be able to give conclusive statements regarding the matter. 



O 



Fig. 12. — Eggs of Clirysops iixxrcns: 

 Four masses on short section of 

 leaf of Spharganium. From a 

 photograph (original). 



