DESCRIPTION AND SEASONAL HISTOEY. 19 



portions. Under the microscope the surface of the egg is very 

 slightly roughened and sculptured. 



Mr. Ainslie, who made a careful study of the egg (fig. 3) at oviposi- 

 tion and later, found that at time of laying the egg was a mere sac, 

 the shell being little more than a transparent, homogeneous envelope 

 or membrane. As segmentation proceeded this membrane became 

 very faintly pitted, and under the microscope with proper illumina- 

 tion barely discernible reticulations, both pentagonal and hexagonal, 

 were apparent. Both ends and sides seemed equally reticulated, the 

 areolation being perhaps a little smaller at the ends. After the larva 

 emerges the shell that remains is a transparent structureless mem- 

 brane with no trace of reticulation. 



The number of eggs placed in a cavity varies greatly, there some- 

 times being not more than 2 or 3, ranging up to over 30; probably 10 

 would be about the average number, although these figures are of 

 course only approximate. Mr. Parks found that during the first half 

 of April the number ranged from 3 to 18, averaging 7 or 8; during 

 the last half and early May the number increased, 25 or 30 being the 

 maximum, with an average of 8 or 9. With reference to the number 

 of eggs that may be deposited in a single alfalfa plant, the one shown 

 beside the hat in Plate I, figure 1, examined on April 23 — at which 

 date oviposition was still in progress and the beetles preparing for 

 oviposition were still exceedingly numerous in the fields — indicated 

 that this plant at this date contained nearly if not quite 1,300 eggs. 

 Of course, in fields where the alfalfa grew up thickly there would be 

 a relatively less number per plant, but these figures serve to illustrate 

 the origin of the countless myriads of larvae that swarm over the 

 plants in an alfalfa field and render more easy of comprehension the 

 destruction shown in Plate III, figure 1. The difference between 

 uninjured and affected plants is shown in Plate III, figure 2, a and b. 

 Other ravaged fields are shown in Plate IV, figures 1 and 2, in con- 

 trast with figure 3 of same plate. 



In the Salt Lake Valley oviposition has been found to take place 

 earlier on the bench lands than lower down in the valley itself. 



Egg-Laying Period. 



The period of egg laying is a matter of considerable significance, 

 since in some degree it will decide the question of efficiency or prac- 

 tical measures of control. As is usual with insects, after a female 

 has exhausted her supply of eggs she dies and there is no second 

 depositing of eggs by her during that season. The actual time 

 required for the individual female to deposit her supply of eggs is of 

 course influenced by the weather. In 1909 egg laying began in the 

 fields early in April, and eggs were found in greatest abundance during 

 the last of May and the first of June. In 1910 egg laying began early 



