136 IOWA ACADEMY OF SCIENCES. 



At the same time, irregular movements of the legs and antennae take 

 place. Soon the pupa skin splits on the dorsal side of the head and thorax, 

 and by the longitudinal contractions of the muscles the dorsulum is first 

 forced out, then the head and antennae, the legs, and finally the abdomen 

 is slowly withdi-awn and the pupa skin remains attached by the claws. 



At first the adults are of a light yellowish green, but soon change to a 

 darker color. Some specimens seem to have great difficulty in starting the 

 tip of the abdomen, it apparently being held by the anal spines. 



THE GALLS. 



The galls are subject to great variations. The typical gall of P. c. 

 mamma has been described by Dr. C. V. Riley as follows: "This gall on 

 the upper side of the leaf is represented by a cup-shaped impression meas- 

 uring on an average 4.5 mm. across, with the outer rim always regularly cir- 

 cular, and not, or but slightly, elevated above the surface of the leaf; at 

 the bottom of the cup a small medium nipple (often obsolete); walls 

 of the impression greenish, the bottom more yellowish. On the under side 

 of the leaf it is much lai'ger than any of the other leaf galls, conical, either 

 slightly narrowing apically, or, more frequently, slightly enlarged. The 

 sides are vertical or nearly so; the top broadly rounded without medium 

 depression or central nipple, size very variable, averaging in height 6.7 mm. 

 and in diameter at base 4.5 mm. Color, pale greenish yellow, with the tip 

 more brownish; surface opaque, rugosely reticulate; at the base often cov- 

 ered with a whitish pruinescence, rarely with a few scattered hairs at the tip. 

 The walls of the gall are hard and woody, at bottom averaging 1.75 mm., 

 and at roof 0.75 mm. in thickness. The cell is large, and in cross-section 

 much more crescent-shaped than in the preceding species." 



The above description is for the typical form for P. c.~mamma. But 

 when the galls are compared we find that the shape and size of the gall is 

 not at all constant. Besides those that are enlarged and rounded at tip, 

 we find a great many that taper gradually to the apex which in some is 

 slightly rounded, in others almost truncate, and in still others slightly 

 depressed. Some have the basal half large and rounded, but at middle it 

 contracts rather abruptly and tapers more strongly to the top which is 

 I'ounded. In another variation the basal half and the apical half are both 

 rounded and subequal, but separated by an acute circular constriction at 

 the middle. In another Jorm the sides of the gall begin to curve outward 

 just as they rise from the leaf, giving the gall a general circular outline. 



By collecting a large number of the galls and placing them singly in 

 little pill-boxes, the adults that issued from each gall could be noted. It was 

 found that P. c-mamma occurred in all the different variations, thus show- 

 ing that these variations are not of specific importance. 



Besides the typical form of P. c.-mamma, a number of variations were 

 found in the galls just mentioned, but as they present such a gi-eat number 

 of variations, and no constant characters being found as yet, no attempt 

 will be made to describe these varieties. 



DISSEMINATION. 



Mention was made of the fact that it was difficult to find the old leaves 

 in sufficient numbers to be of any great value for observation, as they had 

 been carried away by the winds. This is one of the means provided for 



