Spiders and Their Near Relative: 



Sarcoptes ovis. This disease is combatted by dipping the sheep 

 in some poisonous solution. A "sheep-dip" approved by the 

 Federal Government is made of extract of tobacco or nicotine 

 solution and flowers of sulphur. It contains five hundredths of 

 one per cent, of nicotine and two per cent, flowers of sulphur; 

 or, for the first dipping in lieu of the sulphur, more nicotine is 

 used so that the solution contains not less than seven hundredths 

 of one per cent, of nicotine. A second dipping of the infested 

 animal should be made six or eight days after the first, in order to 

 kill the mites that have hatched in the interval. 



Superfamily DEMODICOIDEA (De-mod-i-coi'-de-a) 



The Gall-mites and Others 



In this superfamily are grouped certain very minute mites 



that agree in having the abdomen annulate and prolonged behind; 



it includes two families. 

 The more important 



of these two families is the 



Eriophyidaeor gall-mites. 



The members of this 



family have only four legs 



and these are five-jointed. 



The mites live on plants 



and often within galls. 



Some species produce galls which resemble those made by 



plant liceoraphids in having an open mouth. These galls may 

 g be trumpet-shaped or they 



may be but slightly elevated 

 resembling a blister. 



A common disease of the 

 pear and apple, known as the 

 pear-leaf blister, is produced 

 by Eriophyes pyri (Er-i-o- 

 phv'es py'ri) (Fig. 67). The 

 blisters characteristic of the 

 disease are swellings of the 



leaf, within which there is a cavity affording a residence for the 



mites. Figure 68 represents a section of a leaf through one 



of these galls. Here the leaf is seen to be greatly thickened at the 



diseased part. On the lower side there is an opening through 



93 



Fig. 67. ERIOPHYES PYRI 



O 



Fig. 68. 

 DIAGRAM OF GALL OF ERIOPHYES'PYRI 



g, gall n,n. normal structure of leaf 

 0, opening of gall «, eggs (after Soraur) 



