THE RED SPIDER ON COTTON. 17 
of eggs and developed individuals of both sexes in the usual propor- 
tion. Since ordinarily these virgin females would have deposited 
egos producing males, it is demonstrated by the equal representation 
of female progeny in such matings that the parthenogenetic male is 
completely potent. 
Parthenogenesis has a very important réle in the biology of the 
common red spider. Earlier writers have shown that it works to 
maintain a relative equilibrium between the individuals of the sexes. 
Migrating females very frequently establish themselves without hay- 
ing been fertilized, and they are very likely to be without males 
subsequently. Thus in the event that they arrive unfertilized, their 
offspring will all be male, and upon the maturing of these male broods 
Fic. 5.—a, Cross section of normal cotton leaf; b, cross section of cotton leaf injured by the red spider. The 
puncture is near lower right-hand corner. Highly magnified. (McGregor.) 
the ‘‘pioneer’’ females will at once begin laying fertilized eggs, which 
will maintain the sexes nearly even. 
Feeding and wnjury to plants——AIl stages of the red spider, as 
before stated, feed actively upon the leaf of the host plant. The 
feeding operation is accomplished by means of sharp, slender, lance- 
like mouth parts which are thrust through the epidermis well into 
the leaf, usually on the underside. In the case of cotton, which is 
typical, the puncture is made through the underside. The conse- 
quent siphoning out of the cellular material in the immediate 
vicinity of the puncture results in the impoverishment of the imme- 
diately adjacent tissue (see fig. 5). The parenchymal cells are 
54380°-—Bull. 416—17 3 
