20 



THE STUDY OF INSECTS 



is a cavity affording a residence for the mites. Figure 39 represents a 



section of a leaf through one of these galls. Here the leaf is seen to be 



greatly thickened at the dis- 

 eased part. On the lower side 

 there is an opening through 

 which the mite that started 

 the gall entered, and from 

 which young mites developed 

 in the gall can escape, in order 

 to start new galls. The in- 

 fested leaves become reddish 

 in color but finally turn black 

 and drop off. Badly infested 

 trees fail to develop good fruit 

 and buds are not produced for 

 the succeeding crop. Apple 



trees are also badly infested by this mite. The mite can be controlled 



by spraying the trees with lime-sulphur solution in the early spring before 



the buds burst. 



Among the scavenger mites there are some that infest food products. 



Thus mites arc sometimes found in cheese, in sugar, and in preserved 



meats. 





Fig. 39. — Diagram of gall of PhyUocoples pyri: g, gall; 

 normal structure of leaf; o, opening of gall; e, eggs. 

 Soraur). 



n, n, 

 (After 



Class DIPLOPODA 

 The Millipedes or Diplopods 



The members of this class are air-breathing arthropods in which the head 

 is distinct, and the remaining segments of the body form a continuous region. 

 The greater number of the body-segments are so grouped that each apparent 

 segment bears two pairs of legs. The antenna are short and very similar to 

 the legs. The openings of the reproductive organs are paired, and situated 

 behind the second pair of legs. 



The Diplopoda and the Chilopoda were formerly grouped together in 

 the class, Myriapoda. But this grouping has been abandoned, because it 

 has been found that the Chilopoda are more closely allied to the insects 

 than they are to the Diplopoda. Owing to the very general and long 

 continued use of the term Myriapoda, the student who wishes to look up 

 the literature on these two classes should consult the references under 

 this older name. 



The most distinctive feature of the millipedes is that which sug- 

 gested the name Diplopoda for the class, the fact that throughout the 

 greater part of the 

 length of the body 

 there appear to be 

 two pairs of legs 

 borne by each seg- 

 ment (Fig. 40). 



This apparent 





Fig. 40. — A millipede, Spirobolus marginatus. 



doubling of the legs is due to a grouping of the segments in pairs and cither 

 a consolidation of the tcrga of each pair or the non-development of one 

 of them; which alternative is the case has not been definitely determined. 



