88 THE CANADIAN ENTOMOLOGIST. 



and Syrphids were present in smaller numbers. Numbers of 

 parasites were reared from the larvae and pupae of these predators, 

 among them several undescribed species of Hymenoptera. In- 

 ternal parasites were not in evidence, and only a few aphids killed 

 by them were seen. Possibly in summer they are more efificient. 

 Aside from insect enemies, the most serious foe of the nut-grass 

 aphid is the hard dashing rain, which becomes more frequent in 

 May and June. The fine sand is driven against the lower surface 

 of the leaves with such force by the splashing rain-drops that most 

 of the aphids are beaten off or killed, and after two or three such 

 showers it is often difficult to find more than a few scattered indi- 

 viduals. 



Records of a few individuals more closely observed follow. 

 On January 20 a migrant taken from the field was put on a potted 

 nut-grass plant. While the plant remained fresh apterous adults 

 developed, and by January 31 a number of these were producing 

 young February 2 the original migrant was still producing young, 

 but the plant had begun to deteriorate. February 11 the plant 

 was practically dead, killed by a larv^a of Bactra lanceolana, so the 

 few aphids remaining were transferred to a fresh plant. February 

 19 alate forms began to appear, and between that date and April 7, 

 when the plant finally died from neglect, 181 winged forms were 

 removed, practically all that were produced during that period 

 having developed wings. 



An alate vivipara maturing January 22 was placed on a caged 

 plant. Up to March 6, when she disappeared, she had given birth 

 to 51 young at the rate of one, two or three per day. 



THE SYMMETRY OF INSECTS. 



BY HARRY B. WEISS, NEW BRUNSWICK, N. J. 



All insects are bilaterally symmetrical, or, in other words, the 

 two lateral halves of an insect are alike, and symmetry can be 

 defined as a pleasing equality of parts. Bilateral symmetry is 

 sometimes known as horizontal dual symmetry, inasmuch as 

 bilaterally symmetrical objects are usually oriented from a middle 

 point or portion and exploited by equal movements of the eyes to 

 the right and to the left, which is the natural method. As a result, 



March, 1915 



