s 



CALIFORNIA STATE COMMISSION OP HORTICULTURE. 



among which we find forms beneficial or injurious to our fields and 

 orchards. 



The Crustacea are of little interest to us, except as members of the 

 Arthropoda. The members of this class are chiefly aquatic, and are 



grouped with the insects because the 

 general structure is the same. 



The distinguishing feature of the 

 Arthropoda is that the bodies are seg- 

 mented; that is, they are composed of 

 a series of rings fitted into each other 

 or articulated. In some classifications 

 this class is designated as the Articu- 

 lata, and is made to include the Vermes, 

 or worms, which are also segmented. 

 The latter, however, properly belong 

 in a class by themselves, and the Arthro- 

 poda may be stated to include all 

 segmented or ringed animals with legs. 

 It is by far the most important of all the subkingdoms, and includes a 

 larger number of species than all the others combined. The Crustacea 

 fit the description above and are naturally included in the same sub- 

 kingdom with the insects. 



The Myriapoda come more directly under our view. They are land 

 animals and, in some cases, are very injurious to crops. The centi- 



FIG. 2. A diplopod (Spirobolas marginalus) 

 Natural size. 



FIG. 3. A centipede (Scolopendra heros). About two thirds the maximum length. 



pedes and millipedes are included in this class. Some of these are very 

 minute and others attain great size. One of the smaller of the centi- 

 pedes sometimes appears in vast numbers in damp locations and does 

 great damage to young plants. 



The Arachnida include the whole of the spider family. They are 

 distinguished from insects by the fact that their members generally 

 have eight legs, while insects have but six. They pass through no 



