10 BULLETIN 841, IT. S. DEPARTMENT OF AGRICULTURE. 



DEVELOPMENT OF THE EGG 



After a number of trials it was found to be impracticable to rear 

 the egg in situ, since it was next to impossible to maintain the proper 

 moisture conditions within the stem. The method that finally was 

 adopted, and that gave excellent results, was to remove the egg 

 from the stem and place it in a minute drop of water within a small 

 thin watch glass which was then immediately inverted on a glass 

 slip and sealed with a ring of water to prevent undue evaporation. 

 This form of moist cell proved quite satisfactory and permitted con- 

 tinuous examination of the egg with a moderately high-power lens 

 during the entire period of incubation. It was found necessary, in 

 order to continue the requisite moisture supply during a period of 

 several days, to invert over the sealed cell a larger watch glass and 

 over this in turn a tumbler. In this manner evaporation was re- 

 duced to a minimum. It is altogether probable that the amount of 

 moisture in such a protected cell exceeded that normally present 

 within the grass stem, but in every egg treated in this way the incu- 

 bation appeared to proceed naturally. 



Temperature and moisture are, without any doubt, the prime 

 f actors that hasten or retard the egg development. The temperature 

 maintained within the laboratory during the course of these inves- 

 tigations was much more equable than that in the field, where, as in 

 Utah, the heat of the sun through the daytime, followed by a chilly 

 night, must alternately hasten and check development. The data 

 given below, therefore, may only approximate what actually takes 

 place under field conditions. 



A few hours after the egg leaves the oviduct the milky-white con- 

 tents of the egg which at first completely filled the envelope shrink 

 a little from each end leaving a transparent space or vacuole. Grad- 

 ually the interior mass of exceedingly minute particles coalesces 

 until about the second day when a series of faintly discernible cells 

 arranging themselves along a central axis begins to appear. Early 

 on the third day the form of the larva can be dimly seen, the head 

 being almost transparent and filling one end of the egg sac. The 

 body is looped on itself, the cauda folded beneath the abdomen and 

 extending forward nearly to the head. By the close of the third 

 day the abdominal segments are usually well defined. 



During the fourth day, in most cases, a spasmodic and intermit- 

 tent heart beat may be noticed. These pulsations become more and 

 more regular as the hours pass and during the fifth and sixth, days 

 the heart beats with much regularity at the rate of about 120 im- 

 pulses per minute. At intervals, for some unknown reason, it may 

 slow down to 75 beats, but soon resumes its former rate. 



The head appears abnormally large at this time, but although its 

 general outlines are well defined the brown jaws and eye spots are 



