306 NATURAL HISTORY. 
air down to its diving-bell, coming up every now and 
then to the surface for this purpose. 
520. I have already said enough of the Scorpions 
(§ 509), and on the second group of the Arachnida I will 
spend but a few words. Among the Mites is the animal 
which occasions the disease called the itch, an enlarged 
representation of which you have in Fig. 239. It has an 
oval body, a mouth armed with 
bristles, and eight feet, four of 
which have suckers at the end. 
There is a great variety of mites 
which are found on plants and an- 
imals, and some live in the water, 
swimming about with great free- 
dom. The scarlet Mite of our gar- 
dens has a most brilliant scarlet 
color. The Harvest-men, so ap- 
propriately called Father-long-legs, 
as they have, perhaps, longer legs 
| than any other animal of any kind, 
Fig. 239.—Sarcoptes Scabiei, are mostly very agile. The Book 
or Acatus of the Itch. Scorpions, so called, are little 
Arachnida which inhabit herbariums, old books, ete. 
They are good runners, often going sidewise like crabs, 
and they hunt the minute insects which are found in such 
situations. 
Questions.—How do the Arachnida differ from insects? What is 
said of their food? What of their means of killing their prey? What 
is said of those which are parasitical? What is said of the Scor- 
pions? What are the two groups of the Arachnida? What are the 
two chief purposes for which Spiders spin? What other purposes are 
sometimes accomplished by it? What is said of the cocoons which 
some Spiders spin? Describe the spinning apparatus of Spiders. 
What is said of the compound character of the Spider’s thread? Why 
is it not spun whole? What is said of the mode of its attachment ? 
Describe the foot of a Spider. What is the use of the combs in it? 
Describe its mode of repairing its web. What is known of the man- 
ner in which Spiders transport themselves from one spot to another 
