HiOKoay. 'limbs — hickory-gall aphis. 157 



This last is most frequently the situation which she prefers. Punc- 

 tuiing the part with her beak she causes a profusion of sap to 

 flow from the wound. This evaporating and coagulating becomes 

 organized vegetable matter, which gradually grows upward into 

 a wall around her, and as she continues to puncture it its growth 

 pontinues until it finally closes together over her, and shuts her 

 into a cavity having only sufficient room for her to turn freely 

 around in it. Yet within this cell in which she is thus closely im- 

 prisoned, she is to give birth to several hundreds of young. To 

 make the cavity sufficiently roomy for them she continues to 

 puncture its walls upon every side, thus causing them to expand. 

 Her young also, as soon as they are born, fix themselves to the 

 inner surface of the gall, inserting their beaks therein to feed 

 upon the vegetable juices, thus adding to the irritation and expe- 

 diting the growth of their domicil. Thus as they increase in 

 number and size the gall increases, so as to furnish the amount 

 of room which each requires, without any vacant space between, 

 the whole surface being covered with these young lice. 



It is thus that these excrescences are produced. They are of a 

 globular form and of diiferent sizes, from that of a pea to an 

 ounce ball, and are attached to the side of the stem the whole 

 length of their base, often causing a bend or distortion of the 

 stem, especially when two or three are contiguous and confluent, 

 as they frequently are. The walls of the gall are about the tenth 

 of an inch in thickness, and of a succulent fleshy texture, white 

 upon the inside and green on the outside at first, but soon becom- 

 ing discolored with black, which spreads until the whole is of 

 this color. The hollow inside has its surface covered with minute 

 •smooth shining lice of different ages and sizes, so that it resembles 

 the geode of a mineral, the surface of which is lined with a mul- 

 titude of minute crystals, whose sparkling points are everywhere 

 glittering in the light. Numerous dusky specks are also observed 

 among the lice. These are the cast skins of the lice, all of which 

 moult as they increase in size, their original skins becoming too 

 small to contain them, and being of too firm a texture to expand 

 with the growth of the insect. 



In addition to the dusky cast skins which have been mentioned, 

 in many of the galls numerous round black grains occur. These 



