29 
In the autumn, as a general and almost universal rule, the last brood, 
consists of winged specimens, both males and females. These pair, 
oon after which the male dies; the female deposits her eggs, after 
vliicli she also dies. Early in the spring, as soon as the sap begins 
o flow, these eggs hatch, and the young lice at once insert their tiny 
>eaks into the bark or leaf on which they are situated, and begin to 
mmp up the sap. They wander but little, their entire time being de- 
oted to feeding; hence they grow rapidly, and soon come to maturity. 
This spring brood consists, generally without an exception, of females 
vithout wings. These females, by some strange provision of nature, 
re capable of reproducing their kind without the intervention of the 
nales, and,* instead of depositing eggs, as the last fall brood, are usu- 
lly viviparous, bringing forth living larvae. These are likewise all fe- 
uales, similar to those from which they sprang, and they, in turn, 
troduce a similar brood in the same anomalous manner. This process 
s repeated again and again during the summer and until in the fall, 
hrough some six or seven or even more generations. The last fall 
>rood presents a remarkable change, for it usually consists almost 
ntirely of males and females which acquire wings. These winged 
emales, as previously stated, after pairing, deposit eggs which remain 
iver the winter. 
This is the history as generally given and understood, but more 
areful, recent observations show that in several respects this account 
s incorrect. In many species winged individuals are often developed 
luring the middle and latter portion of the summer; some species so 
ar as known are never winged, yet present oviparous individuals; 
ome species are only oviparous. But the most serious error in this 
I ccount as given is that in the species using this double method of 
eproduction the oviparous female is winged. 
Among the Aphiclinae , on the contrary, the oviparous female is 
pterous, but in some of the other groups it occurs in both forms, 
zinged and wingless. In the former group the winged female is 
ivi parous. 
It was formerly, supposed that this fall brood consisted entirely of 
ormal males and females, but careful investigation shows this to be 
mistake, as there are usually a number of the agamic females among 
hem, showing a tendency to continue the anomalous method of repro- 
uction, which is apparently checked by the approach of the cold 
eason. It has been found possible, by placing the agamic females of 
he summer brood in a situation of uniform and sufficiently warm 
unperature, to cause the viviparous generation to go on indefinitelv. 
have even observed it going on in the middle of winter, in speci- 
lens of the wheat plant-louse (tSiphonophora avenue), taken from 
he wheat while snow was on the ground. Instances are on record of 
his method of generation continuing for four years without interrup- 
ion. 
It is proper to remark that there are some species in which the 
gamic females do not produce living young, but eggs—the reproduc- 
ion, in other respects, being similar to that described. It is also a 
ingular fact that there is an intermediate group, in which the young 
irviu are brought forth in a very thin and delicate egg-like sack. 
