234 ELEMENTARY ZOOLOGY. 



bore, crawl, jump, swim, fly, or may be fixed. The 

 group must be considered as one of the most successful 

 in the animal kingdom. None of the individuals, how- 

 ever, become very large. The lobster and some of the 

 crabs are among the largest. Many are microscopic. The 

 forms that are parasitic are degenerate, and lose many 

 of the characteristics that the independent species have. 



The features that make them especially attractive for 

 study by elementary students are their great variety, 

 the range of their habits and instincts, the beautiful 

 coloration of so many species, the interesting metamor- 

 phosis through which so many of them go before they 

 become adult, and the great importance they have to 

 human interests, both beneficial and injurious. 



251. How many species of this branch did you find on 

 your collecting tours? What percentage of all the species 

 you found were of the branch of arthropods? Did you 

 find representatives of each of the four main subdivisions? 

 How many different modes of life did you find represented 

 among them? 



252. Field Work on Spiders: a Practical Exercise. 



After examining several spiders, state how you may 

 always be able to distinguish a spider from an insect by 

 a study of the exterior? After a period of study in the 

 field, let the students report on the haunts and place of life 

 of as many kinds of spiders as have been found. Do any 

 live under boards and stones? Do any burrow? Do all 

 kinds spin webs? How many different kinds of webs are 

 you able to discover? Are they equally regular and 

 complex? Determine by observation, if possible, to 

 what various uses the web is put by different species of 

 spiders? Learn to recognize the spider which produces 



