208 Illinois State Lahoratorij of Natural History. 



ance of the male, and (4) what connection, if any, exists be- 

 tween the form on the roots and that on the leaves. The ob- 

 servations given below answer the first three of these queries, 

 but I am not at present able to give any definite results con- 

 concerning the obscure subject of the origin and fate of the 

 aerial form. 



Field Observations. 



The first observations during 1887 were made in an oats 

 field, on the University farm, that was last year planted to 

 corn and abundantly infested with corn root lice. Two hours 

 were spent, April 21, in searching the formicaries of the 

 common brown ant (Lasiiis alienns) and of a larger red ant 

 which was quite abundant, but neither plant lice nor their 

 eggs were found. The Lasius were burrowing about the 

 young oats plants, which had been up a week. April 25 I 

 repeated the search, and found a mass of about fifty plant-lice 

 eggs slightly below the soil surface in a Lasius nest. They 

 were mostly green and nearly ready to hatch, and some of 

 them put in a dry vial disclosed several young lice the follow- 

 ing day. On April 29 another lot of aphid eggs, together 

 with young lice, were found in another nest of Lasius alie)ius 

 in the same field. 



The young lice were on the radicles of the sprouting seeds 

 of smartweed (Polygonum incarnafum) and Setaria, the earth 

 about which had been mined by the ants. On May 4 larval 

 lice were abundant on the plants just mentioned, always at- 

 tended by ants. The majority of them were about half grown, 

 but no adults were seen. By May 16 the stem-mothers bad 

 become adult, given birth to young, and largely disappeared, 

 though a few were still present. The prevailing form then in 

 the field was the young of the second generation, a few of 

 which had become pupse (of the winged form), but no winged 

 adults were seen. Ten days later the corn lice had, so far as I 

 could judge after an hour and a half of diligent search, com- 

 pletely disappeared from the field. 



The second field under observation had been in corn for 

 years and was again planted to corn last spring. I first exam- 

 ined it April 29 (before it had been plowed), when young 



