THE AEACHNIDA. 299 



its metamorphosis. What is said of its eggs ? Describe the arrange- 

 ment of the proboscis. What is said of the Musquitoes in vaiious 

 regions of the earth ? What is said of the order Aphaniptera? What 

 of the order Aptera ? 



CHAPTER XXX. 



THE AEACHNIDA. 



508. The second class of the Articulata is that of the 

 Myi-iapoda, the Centipedes, § 388. This I will not dwell 

 upon, but will pass directly to the third class, the Arach- 

 nida. This class was for a long time included among the 

 Insects, and Spiders are very generally spoken of now, 

 in common conversation, as belonging to that class ; but 

 the Arachnida differ from Insects in several important 

 particulars. The head of Insects is distinct from the 

 chest, but in the Arachnida the head and chest are united 

 in one ; and this is called the cephalo-thorax. Insects in 

 their perfect state have but six legs, but the Arachnida 

 have eight. The Arachnida have not the compound 

 eyes of Insects. Again, the antennae of Insects are want- 

 i ng in the Arachnida. 



If 509. The Arachnida are carnivorous ; but generally, 

 instead of eating their prey, they suck the juices from 

 their bodies. Many of them have a poison apparatus, 

 by which they can destroy more readily those victims 

 whose strength would otherwise be too much for them. 

 They have mandibles and pincers very much like those 

 of insects. In those which are parasitical — that is, those 

 which dwell on other animals — the mouth has the form 

 of a trunk or proboscis armed with a kind of lancet. The 

 Scorpions have a curved and pointed instrument at the 

 end of the tail, as seen in Fig. 233 (p. 300). They have 

 large claws, like those of the Lobster, with which they 

 seize their victims, and then pierce them with this curved 

 sting, which is armed with poispn from a gland. 



